ill also add that IF its not lc, you could just shrink a random cars model(i know it can be done) to fit a motorcycle. but that will just flip you over everytime you try to move (cars dont stay horizontal by default, remember? ), so yes. its probably lc.
as for the the topic starters questions:
-there are deathmatch(just a random free for all) and stuntserver(no wapons, just doing stunts. there are even some custom ramps around). that though, doesnt stop you from doing whatever you want; mta doesnt have rounds, and all the map is opened, so practicly you could do anything you'd like to do. you can even orgonize people to help you roleplay, or do team matches.
-in the current version, lag is still an issue. theres a thread somewhere that will tell you how to shoot right at people. but other then that, the gameplay is smooth.
-games last as much as you want! freedom of gta lets you do whatever you want, whenever you want
any more questions?