Hm, these are the kind of questions that I'm not very good at answering, I'm sure you'd get better replies from the veterans on the UA forums (ua.reonis.com), but I'll try ...


1. I just tinkered a bit with the Game Settings of Vanilla UA and it seem that there is no level cap for humans apart from the general level 40 cap. I can't say anything about level progression above lvl 20 though and how it is implemented into UA, whether it's fun at all to play such high level characters. I think the other races are capped at very low levels, partially below lvl 10 even (?). Hacking allows you to remove the level caps for all races though, so there's a chance you don't have to worry about level caps in hacked designs, if a mod author didn't like them.


2. I completely forgot about that, that's a question I was searching the answer for myself, in order to add it to the sticky. There probably is a design like that - it would also be very easy to create one with the editor yourself, in a matter of minutes - but right off the bat I can't remember any. In a well-made design you wouldn't need to prepare your characters like that either, as the author can set the experience, gold and level of equipment you get during character creation, so if a design is meant for e.g. a party of lvl 12 characters, usually creating new characters should automatically set them to lvl 12. But I take it you're more interested in playing around with the characters for fun than in the practical side of it? The module list at frua.rosedragon.org offers these, but I haven't tried them myself, so I can't vouch for their quality:

Trainer + Mega Trainer by Chris Elion:
"Two separate trainer modules, each with arenas and shops. Perfect for building up your levels."

Training Camp by D.W.Gilbert
"A one-dungeon module intended as a n ice place to keep your characters between adventures."

Keep in mind that transferring characters from one design to another might not worked well (and lead to bugs) with hacked designs unless they're from the same series.


3. No idea, sorry; but that's probably because I wouldn't find them very interesting myself. ;)


I guess it's not quite what you're looking for, but the Realm series by Ray Dyer has a hub module, basically just the maps of the Realm that you can travel across to learn what adventures are available in the different regions, and then you'd have to transfer your characters to that particular adventure design you want to play, so it comes close to that library with info about other adventures you were asking about, only that it's restricted to the ~40 Realm designs. That hub module which also serves as an intro to the series (and includes a few mini-missions) can be found (and more info on the series [url=http://therealm.flopsyville.com/Menu.htm]here).

Oh, and there is also The FRUA Hall of Fame by Jacek Dobrzyniecki, which is kind of a meta museum/library design about other UA authors, but I'm not sure whether it would be of interest to new players not familiar with the community and its members.