Welcome to the forum!
What you're actually looking for is the
Suggestions Board, which Toady reads and occasionally comments on. Usually, though, he just notes down things that he agrees with stays silent.
Make sure when you go to that forum that you do a search for the topics that you're suggesting. Most topics have already been suggested in one form or another, and it's usually best to see if your specific idea has been talked about before bringing it up. Not to say you can't add to an existing discussion if you have more to add, but we don't want to waste Toady's time with hundreds of suggestions all saying the same exact thing. We'd rather he spent the time programming.
Two address your two specific suggestions, however:
1) Toady has said that he specifically does
not want the player to be able to do that in Fortress Mode, although you may be able to do something kind of like that in the Army arc for soldiers sent away from the fortress.
2) There are lots of threads on the suggestions board regarding sieges and how to make them more interesting. Do a search there and read through the threads, and feel free to add in any new thoughts you have after you've read them!
Oh, and don't be afraid to necro threads in the suggestions forum, it's considered better to have a few consolidated threads then a bunch of scattered ones.