I ride H/J. You certainly can ride in breeches and paddock boots, although it might be tough to find breeches long enough. Most breeches for adults stop above paddock boots-although that might just be because I'm 5'10"
It's also not very comfortable as the stirrup leather can pinch. You can school in half chaps, paddock boots, and breeches which looks nice and is comfortable. You can get used paddock boots and half chaps for pretty cheap-look on ebay
or the classifieds on this website.
Dress boots are meant for dressage and a too big calf can certainly be a problem when jumping. That would definitely affect your grip and position. Tall boots are meant to be pretty form-fitting, which is why most have a zipper in the back, so it can fit the curve of the calf better.
I've seen some of the bootcut riding tights, but honestly never on anyone under 50 y/o. If that's you and that seems more comfortable, then go for it! But if not, it's not really something you see often. I also think that would be uncomfortable because the stirrup leather would pinch.