Anyone remember the Dogs of War server? I made a mutator back then that replaced the teleporters at the end of maps with a trigger that merely ended the match. This allowed for mapvote to be used. I still have that mutator, so I could modify it to load another mod after NP35 is finished.
I'm not sure I'd want mapvote on this server though, I've been loving the old ONP style. I wouldn't want to break up the order. (Atleast give ONP so more time. We could always add in mapvote later on.)
Postal, about the maps: the things you described were how most co-op maps are. It isn't like MH at all, it is about cooperation and ammo conservation. Players that have been playing for a few maps should have their own ammo already filled up since it all carries from one map to the next. Single playerstarts aren't bad at all, telefrags are prevented somehow.
I do agree about having an ending map. I have ran the Credits map online before and it doesn't have very many issues online other than not ever ending.