Matt VDW, to answer your questions :
--- "Do you have classifications based on skill and/or weight, or are the fights "open"?"
Depends on the venue. This fight is a local club fight, which is a warmup for serious competitve amateurs and a way to break in new fighters. Experience is definitely considered when matching up opponents, and we use the same weight classification of amateur boxing sans cruiserweight.
---"Do you wear any protective padding"
Yep, shin guards, gloves (16 ouncers for me), and headgear. This is more of a nuisance than it is a benefit. When a fighter steps up to semipro or sanctioned amateur fights, we ditch the head gear and shin guards.
---"How long do the fights last? Are they usually decided by points, or by one fighter being punched/kicked into submission?"
Fights last three rounds, three minutes each. Fights are decided just like in pro boxing, an opponent wins by a KO, TKO, or judges decision. Since these are only three round fights, most end up in decision.