1. Yeah its kinda annoying... Brahmin rams you, rocket merc goes "HEY! *BOOM*" All other mercs go berserk.
2. Absolutely this is pretty much a fact, they do seem busy almost all the time..
3. ... I don't get this one. They come locked, thats why he gives you a key, but yeah you should be able to buy a replacement from him, make things ALOT easier.