1. You can get on a trike and ride it without any training, although you'll need to learn how it corners and lean into the inside off the corner to some degree if you are going very fast!
2. Two wheel 'bents are so diverse it's hard to generalise, but you will need to learn how to balance any of them at low speed. It took me a while to stop and start on my AZUB-4 without the occasional topple over.
3. I found the tops of my thighs ached after riding for the 500 or so miles, you do, in my experience,
(As a 'bent owner since 2005 and 'bent only rider since 2008.) use slightly different muscles, but if you're generally fit, rather than specifically DF fit it won't be an issue.
4. Recumbents are fun, they attract attention both parked and in motion. Fit a small flag or better yet a pole with fluorescent ribbon lengths attached, this is not to attract the attention of the vehicle behind you, but the one behind that, so make it high enough to be seen through the windows of a car. Expect people to want to talk to you about your 'bent.
5. Recumbents are safer than DFs. When I was riding both I was always stunned by how damned close cars passed me on a DF compared to the wide passes that are routine on a 'bent.