Best Transport Option for a first time traveler in Paris

The ticket t+ is good for one trip, in one direction, anywhere the metro/bus travels. Metro use has nothing to do with zones but there is no metro anywhere in zone 4. To reach Paris, you will need to either use the RER or bus. RER tickets are sold point to point.

One solution you might consider is a zone 1-5, 5 day Paris Visite Pass. Cost is 65.80€, not the cheapest possible solution, but definitely the easiest as it takes you anywhere in the Île de France where you might want to go.

What day are you going to Versailles?

If Monday or after, you can buy the Navigo Decouverte for that week, 28Euros, and use other ticket options before.

I hope you mean arrondissement 4 which is in zone one and not zone 4; it would be an enormous mistake to book lodgings so far from Paris for a trip to Paris. If you are actually in zone 4 then you are probably one of the rare people who would benefit from a Paris Visite Pass which while expensive will cover you in all 5 zones and can be bought for any 5 consecutive days. That way you can make the long commute to Paris and then use the metro in Paris all day each day of the 5 days you have it. It would of course cover Versailles and trips to the airport as well.

Wish we had taken a taxi from airport, train was packed worse than those in Japan. Unbelievable and we have here many times , never experienced such a frightening situation, esp with Covid still lingering.

Erm, where in zone 4 are you staying? It's a gigantic area, and let me tell you, some parts aren't too great. With a stay that straddles two calendar weeks, you'd definitely benefit from a Paris Visite - a sentence I'm not sure I would ever write!

Thanks all...I am going to be staying in Stains (Zone 4 very close to RER D station).Distance wise it shows as 20 minutes from the city centre hence thought I will book that.

I sure would not stay there but if you are staying there then the 5 zone Paris visite is definitely the transport option you want for your dates. It will take you anywhere in the ile de De France during its duration and it can start any day --

Stains is a lower-middle class suburb, from a safety standpoint it is not the worst (I am not aware of any specific issues in Stains, surrounding places like Épinay or Garges are worse) but the northeastern quadrant of the Paris area is generally not the best on that front. Make sure to watch your stuff and your surroundings if you're on the D train late at night, especially if your group is female-only (and in the latter case, I'd consider taxis/Uber after 10 PM or so).

With the T5 tram or the D train you'll be very close to Saint-Denis: take the opportunity to visit the Basilica, it is a great sight.
When going from Stains to Versailles, pack a lot of patience: it will take about 2 hours one way.
As for "20 minutes to the city center": in practice, 30-60 minutes is more realistic, because you'll have to walk to the station, wait for train, exit arrival station (or change to the metro at Les Halles if your destination is further afield).

EDIT: with your trip being on 30 September, in the middle of Paris Fashion Week, and likely cancellation fees with Airbnb, I guess any advice to "stay elsewhere" is not practical. Had you asked months ago, I would have advised to do just that, but in this case, as long as you manage expectations and exert caution, it will work out. After all, literal millions of people regularly commute to Paris from places like Stains.

And last but not least, look up how to pronounce Stains ;) . That nasal "ain" is hard to describe, I guess it sounds a bit like "stung".

One of the cruelest jokes played on inexperienced travelers is the 'it is only 20 minutes from (town)' canard. It can easily take 40 minutes to go to an attraction across town when you are in Paris. We often stay in a friend's place in the 13th and it has literally taken us 40 minutes to get to a location on the other side of Paris.