You are fit enough... extra gear? None really, dress for the weather as you would on a 100 and remember it might be a little colder at the end due to end of the dayness.
For my money longer rides are about *conditioning* - saddle comfort, what you need to eat and when, wrist aches, how fast to go (or not), whether you need company or want to ride alone (or a mix). You won't get any of that knowledge by staying at home!
And on a 200 you will a almost certainly have a dip at some stage - well I do. Don't panic, have something to eat, slow down for 20 minutes, work it through without putting yourself in a big hole. You can recover on the bike.
The main thing that will trip you up is self expectation! Lower your expectations about speed and just spin around and you will be fine.