First time in Australia

Mondumo is owned/run by Colin Mairs, a Rick Steves tour guide using the RS template, and often mentioned on the forum.
https://mondumo.com/tours/australia-in-14-days-tour/

My country is very big and very diverse so can you give me an idea of what you hope to see and do?

I traveled around Australia back in 2010 with pretty much just a Lonely Planet guidebook.

My biggest tip for a first timer is that because of its unique plant and wildlife and concerns about biosecurity, Australian airport customs is MILITANT about bringing in any kind of food. Got my homemade trail mix (which had no raw seeds) and a sandwich (from the plane!) confiscated.

I see David Willett is the guide for the tour mentioned for next October. He has been a long time RS tour guide. He was my guide on the best of England tour in 2022. He was fabulous. I wouldn’t hesitate to take that tour. Looking at the itinerary, it has RS philosophy all through it.

You could save yourselves quite a lot of money if you were willing to do some of the planning yourselves.
Booking airfare and accommodation is pretty straightforward. Once in the country you could craft your own itinerary by relying on local day trip and tour providers to see whichever sights interest you. Perusing any good guidebook will give you some ideas regarding destinations and attractions.
My suggestion for a first-time visitor would be Sydney (beautiful), Cairns and the GBR, and maybe Uluru. Qantas has a low-cost affiliate called Jetstar that makes it pretty easy (and cheap) to get around the country.
As has been said, Australia is a huge country so concentrating on just a few areas should be a priority ... depending on exactly how much discretionary time you have at your disposal.

We didn't go to Uluru, but I loved Melbourne because of the little penguins and two beautiful parks-the Botanical Gardens and Fitzroy. And I will admit that I loved Hartley's Crocodile Adventure in Cairns-we got to feed kangaroos and pet a koala(which I know is not allowed in many parts of Australia, but I don't see the harm to the Koala sitting in his tree munching his eucalyptus).

We visited Australia twice and loved the country.
It is huge. On our first trip we flew into Sydney from LAX on a 14 hour flight, then had a 5 hour flight to Perth. Perth is on the West Coast and we had a cruise (Over the Top of Australia). We spend some 3 days there before the cruise that visited several ports in Australia as well as two days in Bali, Indonesia.

Darwin was interesting and historical as well as Cairns, Brisbane and Sydney. You can do the Great Barrier Reef from Cairns.
We spend five days in Sydney after the cruise and did the Blue Mountains on a day trip as well as a visit to the north of the city to vineyards that were nice.
Lots to see in Sydney, do the Bridge Climb either the expensive one with a guide or just the piles on your own. Go to Bondi Beach on a day tour that included the Botanical Gardens. Do a Harbor cruise and visit the Opera House for an opera. Do go to the zoo.
Also, there are museums in the city that are special.

The next trip was a few years later and we again visited Sydney, but also spent several days in Melbourne, from there taking a two day tour that included The Great Ocean Road and the Philips Island penguins. Also, did another winery near Melbourne.
Melbourne is interesting, visit the site of the olympics and other sites.

You can do stuff on your own, language is no problem and Aussies are very friendly and helpful, but take some local tours as well.

On our second trip we also did 9 days in New Zealand and later took a 23 day transpacific cruise from Sydney to Seattle that was wonderful.

I've had 3 visits to Australia within the past 6 years. It is a very easy country to DIY if that is at all an option for you. No problem with language(!) and in addition to public transport in the cities, the major tour areas have many day trip, private driver/guides, and tourist shuttles if you don't want to rent a car. (I did not have a car on any of my trips.)

The best advice you have above is the of Eatsrootsandleaves - if you indicate your interests, you can get more specific help. Lots of options!

I'm just going to mention one spot which (to me) always seems over-looked by Americans - the capital of Canberra. I've spent multiple days visiting museums, hiking along with kangaroos and finding platypus - all with public transport, Uber, and an occasional guided day trip. After my first trip, I had to return for more explorations on my next Australia visit.

One thing to keep in mind is that Australia is huge with large climate differences. Take this into consideration if planning a multi-region visit. You may want to avoid the Great Barrier Reef (Cairns, Port Douglas, etc) in the rainy season for example.

This link explains season in general:
https://www.australia.com/en/facts-and-planning/weather-in-australia.html#:~:text=Australia's%20seasons%20are%20at%20opposite,rainfall%20in%20Australia's%20capital%20cities.

Some info for specific cities:
https://www.australia.com/en-us/facts-and-planning/weather-in-australia.html

Had a quick peek at the Mondumo tour mentioned above.
Like this bloke's NZ tour it is absurdly expensive. Gonna cost 3 adults 24 grand before any other expenses. All up meals, optionals and airfares this family of 3 adults would be up for more than my yearly salary for a crappy 12 day 13 night tour.
Don't really care if the guide is the best bloke on the planet the tour is ridiculously expensive and the itinerary seems a bit dumb. Why start the tour in Melbourne, spend 3 nights there but do sweet FA while there then fly nearly 4 hrs to Cairns? You pretty much blow a whole day and it adds to the already ridiculous price.

I hadn’t heard of the company the OP mentioned. They seem a bit more reasonable price wise but there were a lot of different tours listed so I haven't checked them out too closely.
Connie didn't say which one she is considering

Yes ORD Canberra gets forgotten particularly by American tourists. From Canberra Kossie and the Snowy Mountains is an easy visit as is the gorgeous Bateman's Bay area.
You've done well to spot platypus too, most Aussies will have never seen one in the wild. Lucky me, I will likely have a close encounter Monday on my routine kayak training session.

Eatsrootsandleaves, thanks for your comments! I know I felt very privileged to see the platypus in the wild, but didn't know that many Aussies have not been so lucky.

Connie - My experiences are an example of what I could easily do DIY. Australia trips have been among the easiest I have ever planned and executed.

The platypus sighting was in the Tidbinbilla Nature Reserve shortly outside Canberra. One could probably Uber if you make arrangements for a return, but I booked a half-day tour with hotel pick-up. As well as platypus,we rode electric bikes along with kangaroos! And, if a traveler is more into science than nature, we stopped at the Nasa Space Center Canberra Deep Space Communication Complex.
https://www.tidbinbilla.act.gov.au
https://www.viator.com/tours/Canberra/Canberra-Half-Day-Afternoon-Wildlife-and-Electric-Bike-Tour/d81965152P6

So excited for your plan to visit Australia! My husband and I recently returned from ~ 3 weeks in Sydney. Our jobs allowed us to take rare time off over the holidays – their summertime – with great weather but vacationing crowds (ugh). When would you like to go? What would you like to do?

Sorry I do not have a package tour to recommend; it was easy for us to DIY on this and a previous trip to Western Australia 1 ½ years ago.

We booked rentals, splitting our time between two Sydney suburbs: Coogee Beach (Eastern suburb) and in Manly (north of Harbor), because we are “ocean people” who like to swim and explore coastal walks. Visiting Sydney’s Central Business District area for sightseeing and learning about the city’s fascinating history was easy via convenient public transport. The frequent ferries are fantastic!

Re: cheap plane flight tricks, please use caution if you use JetStar. We had an unpleasant experience with them on Jan 2 when our flight to Honolulu was delayed two hours. The delay made us miss a Hawaiian air connection to LA (peak season, oops). Neither JetStar nor Hawaiian Air would help us. We found out from our Melbourne friends that this airline is also known as “Cr*pStar.” We prefer Qantas, which runs frequent sales, and we have booked with miles on American’s website. Our JetStar fare was half the price, and we got what we paid for!

Yes Jetstar have a reputation. My last Jetstar booking didn't go well. Our 9 am flight eventually became a 1 am flight that departed at 2.30 am.

On the other hand, we've flown Jetstar about a dozen times in the past - crisscrossing Australia several times - without any drama whatsoever.
It's a no frills airline that doesn't pretend to be anything else, but has always gotten us where we wanted to go at a substantial cost saving versus any of the legacy carriers
Might add that we've flown the Honolulu to Sydney route a couple of times but made it a point to grab exit row seats for the extra legroom. Wouldn't have wanted to ride in the back for the 8+ hours - it'd be a very tight and uncomfortable squeeze on a long flight.

Statistically Jetstar sit right at the average mark for reliability about equal with Qantas at 68%. They have been investing heavily to improve their service in recent times.