Florence/Cinque Terre

We'll then head to Cinque Terre for 4-5 days ...........Is this a reasonable itinerary?

Unless you are avid hikers that may be more time than needed for CT, unless you just want to 'chill out'

Good to know. We love hiking but are concerned we might get bored with 4-5 days in CT.

We thought about reducing our Ireland leg of the trip to (4-5 days instead of one week), and going to Palma De Mallorca or Barcelona too. But don't want to overextend ourselves either.

A lot depends on how the number of days shakes out and where you fly from. If Pisa in the afternoon (not early am), you can depart form CT or Florence the morning of.
I would give CT three or two full days, so three or four nights. You could add the days to Florence or add a stop in a smaller place. Lucca is very popular (I liked it okay). Barga is a town in the mountains near Lucca that is very nice also. You have many options all close together that could fill the days if 4-5 is too much hiking.

I congratulate you for already being willing to limit your stops to only a few in 8-9 days in italy. CT as mentioned my not need 4-5 days. But arrival day with the train to Florence is one full day gone. Day 2 will end up being a light duty day since you will still be recovering... maybe schedule two museum visits (AM and PM) with tickets ahead of time and get nice lunch and to get to bed early. The trip to CT will be one morning (1/2 day with packing, traveling, checking in), and you will want to be located in your departure city the night before you leave unless it is can afternoon flight. You can easily fill all of your time in Tuscany. Or add a day trip to Siena and back to Florence to sleep.

Have fun.

Thanks! Good point as our flights to Rome is 9 hrs so recovery will definitely be needed.

Our goal is to plan a late evening flight to Cork or Dublin (I see some as late as 9pm from Pisa) so that our departure doesn't take a full day.

This is our first time travelling to Europe,

Would be a shame to land in Rome and see none of this amazing city.
I'd take 2-3 days from CT and spend those in Rome

I'm definitely worried we're making a big mistake by not spending much time in Rome. But I've heard from a ton of people that Rome can be incredibly overwhelming, so I'm a bit worried about starting there & wondering if it may be better for a second Italy trip. We recently had family move to Ireland, so likely will be going to Europe more frequently now due to this. Honestly no more expensive than visiting family in Newfoundland & Labrador!

One more question for folks. Do you recommend we opt for CT? Or go elsewhere that may be a little less crowded? Worried a bit about the extent of the crowds & want to make it an enjoyable experience. Open to other areas such as Camogli, Genoa, Rapallo, etc.

Worried about encountering a situation like this:
https://www.cittadellaspezia.com/?p=232882

Since you plan on making future trips to IT spend your first four nights in Rome since you’re landing there. If you take a train from Rome’s airport you have to transfer at Rome’s Termini station before going to Florence so stay in Rome since a connection is involved. From Rome’s Termini station you can take a direct train to the Florence SM Novella station (1h 45m).

Could you clarify a few points.....

If I'm reading the information correctly, it looks like the overall duration of your trip is about 16 days, split between 9 days in Italy and 7 days in Ireland. Is that about right?

I also live in western Canada and have made that trip so have a good idea what your experience will be like. As this is your first time travelling to Europe, you'll lose the first day in travel and will arrive in Rome the day after you depart home.

It's unfortunate that you won't have time for even a few days in Rome, but with such a short Itinerary, it's probably better to focus on the two areas you most want to see. Allow for at least half a day (sometimes more) in travel each time you change locations.

Most of the trains between FCO and Florence require one change at Roma Termini. Your travel day is going to be very tiring so hopefully you can get some rest on the flight. There are some potentially expensive caveats to be aware of when travelling by train and other public transit in Italy. You'll encounter this for the first time on the Regionale train from FCO to Roma Termini. If you need further information, post another note.

Determining how to portion your time between Florence and the Cinque Terre will depend on what you want to see in each location. If you don't have one already, I would highly recommend packing along a copy of the Rick Steves Italy guidebook to help in your planning. Which of the five Cinque Terre towns are you planning to stay in?

As you're planning to head for Ireland after your Italy visit, the Cinque Terre is a good choice for your last stop, as it's reasonably close to the airports in both Pisa and Milan.

Were you going to rent a car in Tuscany? There are plenty of coastal areas with hiking comparable to CT but better with a car. Camogli is not one of them, it is a snap without a car and the hiking is much less crowded.

We're not planning on renting a car in Tuscany, but will be going through a small group tour or private driver for the wine tours.

Any suggestions for hiking options similar to CT?

Any suggestions for hiking options similar to CT?

You already pinpointed it--Camogli. It's on the train line, as is neighboring Santa Margarita Ligure. Between them sits Portofino park, and you can crisscross it by hiking trails and use ferry and bus to supplement hikes. Rapallo is larger but close, and it has a cable car you can go up for stellar views.
If you don't mind being "stuck" (so to speak) without a car, I love the Lerici-Tellaro-Montemarcello area. You can get off train at Sarzana and take a bus or taxi to Lerici or Tellaro. That park is named Montemarcello. You can get there fairly easily, but you'll be reliant on feet, bus, and taxi while there. If you wanted to get away and just hike, it works.
CT gets very crowded to be sure--and I often suggest alternatives for that reason, but if you are staying within one of the villages, you gain advantage of having it in morning and evening, and ideally you will be on the trails during the day when it is most crowded.

I've heard from a ton of people that Rome can be incredibly overwhelming, so I'm a bit worried about starting there

I would say it is 'overwhelming' in the sense that a huge candy store is; so many many treats to choose from. You cannot have them all, but have to choose a few and enjoy. You will not be able to see everything, so choose a few things and enjoy. And as you make more trips you can whittle away at the the list of things.
Do not avoid Rome for fear you won't be able to 'do all of it'. Like a pie, enjoy a slice at a time.

We loved CT but two nights was plenty. We had a full day to explore the villages (by train and boat) and two wonderful evenings. Perhaps you could add Lake Como for a few days and not be too far from a flight from Milan?

You could stay in Genoa for the CT time and make day trips to lots of other Ligurean towns from there including CT. Rapallo is lovely as well. I myself will be spending September in Genoa and then going to Chiavari after for two months. Planning on exploring more of the Ligurean area in that time...You can then fly to Ireland right out of Genoa!