Dangerous waters doesn't look too bad, but i'm saving my game budget up for silent hunter 3 (my weekly budget for games is low, so in a year i should have enough lol)
and yes, they all have different stats: the deck gun, AA guns, no. of forward and rear torp tubes
you can check out the stuff @
Enigma's Home Page - Warfleet.net
its in the factions section, it has a full list of all the subs and surface ships (cept the german MTB, i don't think its on there yet)
and they all look very different, the salmon has its con tower inclosed and forward of midship, the LFN sub is BIG, and the U-boats are sleek and rustic, in the Type 7's case, rusty

for a peice of WW1 junk they are pretty good
and i doubt anybody would mind you asking questions, since none of them have been stupid/painfully obvious, you'll be right buxton: