We used Ryanair to fly from Paris to Rome, and because we understood all the facts about where the airport was and luggage prices, we were very satisfied with the whole process.
It is cheaper to pay for your luggage fees while making your reservations. You can't go back later and add it. I also bought our bus tickets to the airport online before we left home (on a different site).
We had our hotel order us a taxi the night before because we had a 9am flight and needed to leave Paris at 6am. The taxi was there right on time --about 5:15. That turned out to be a little early because it didn't take long to get to the bus stop from our hotel on Rue Cler. We actually were able to get on an earlier bus since we got there so early.
A lot of people complain about the bus ride to the airport but who wouldn't enjoy a ride through the French countryside? Since we didn't go anywhere in France but Paris and Versailles, we were glad to get to see it.
You will be dropped off right at the terminal door. If you decide to wait until you get to the airport to pay your luggage fees, as you go in the small terminal, go to the window at your far right. You will need to pay your luggage fees first before going to the ticket window. Even though you have bought your airline tickets, you will still need to go to the ticket counter but you can't do that until they list it on one of the overhead signs above each counter.
You will have time to kill and they have a nice coffee shop right by the ticket counters. You will check your luggage (unless it's tiny and you can carry it on) and you will show your luggage fee receipt at this time. Now you can go through security to the gates.
There are only 4 or 5 gates--it's a really small airport-- so everything is easy to find and close. There are a few shops, restrooms and a coffee counter in the gate area. You will watch the signs over each door to know when to board your plane.
Hope this walk through helps.