Your legs will ache for your first few long rides but that'll pass as you get more rides in.
Kim is right don't apologise for zooming off the front downhill to maximise momentum up the other side. Riders on road bikes can cut across you too soon as well. I think they see your head and equate that as being near the front of the bike, when clearly you've got your legs out in front of you. A robust shout will stop that if you're riding with them.
If I'm going to ride with a group I usually explain some of the things to watch out for that they might not have thought of. On audaxes I usually let everyone head off first and start at the back. The silly riding if often in the first few mins of getting going.
I've got the Easter Arrow 400 this weekend. We are a recumbent, fixed, tandem, geared road bike. A team event. We all know each other, so should be fun, but we'll still have the pre ride chat about the different characteristics involved with each bike.
Yes I'm finding my recumbent a great long distance ride. I'm also finding in the more stretched out riding position that digestion has not been an issue so far and I can ride further between feeds (than on my road bike). As for lack of pressure points, a delight.
Good luck with your first 100. Don't leave it too long. You won't find it too hard, having done up to 400 on your road bike.
As for handling. Now I'm just relaxed back in the seat with a light hand and don't even think about it, the stability is rock solid. Riding one handed is now easy.