300-sub-350 is more than sufficient for indoor play. Still pretty ouchy at contact-5ft but enough so a longer shot can still be felt/heard.
Setting things to semi-only, ammo limits per mag and no minimum engagement distance really help to both keep things moving along and to head off guys spraying rounds endlessly from static positions. Same with total ammo limits if you've got more space to play with.
Those types of conditions may not appeal to everyone, but give them a try and assess what effect it has on game play.
Floor surface also makes a big impact. BB's on hard flat surfaces make for wicked wipeouts (mandate boots with good treads)...gravel makes for bad slides and road rash...sand gets into everything...dirt (outdoors) turn into mud and icy mud in the winter. Brian's place is kind of lucky in that the cracks in the floor boards is a natural sump for BBs...and even then by the end of some nights it's a virtual carpet of BBs, especially with grenades and 40mm's
Basically figure everything is going to get shot eventually...lights/windows/signage/etc... Can't beat hard cover vs. netting/etc...