"A barrage weapon may not target a unit outside 36" during nightfight, irrespective of the fact that you do not need LOS, right?" Correct.
"The only question mark for me would be black sun filter with Tau, as i'm not sure how that is worded." Blacksun Filters grant the Night Vision special rule, which allows the unit to ignore the effects of Night Fighting. Matt got it.
"Can you use Feel No Pain on a Perils of the Warp result?" As written, yes.
"What is the cover save on top of a bastion?" Ambiguous. Decide with your opponent before the game begins.
"For a regular & heavy venom cannon there's a -1 applied to the vehicle damage table. Does the -1 also apply to the building damage table?" I've previously ruled that shooting at buildings is exactly like shooting at vehicles. All other modifiers to the vehicle damage table (from high AP weapons) are identical on the building damage table. With that in mind, I believe that the venom cannon is supposed to have a -1 to rolls on the building damage table. Since that's not strictly RAW, though, you should mention it to your opponent at the start of each game, and 4+ the issue if necessary.
"Can the Eldar Vibro cannon hit a flier?" Congratulations! You've found a line weapon that rolls to hit! When applying the vibro cannon shot against a flyer, treat the attack rolls as snap shots (ie, unless one of the cannons in the battery rolled a 6 to hit, the shot is treated as having missed the flyer). Apply results against non-flying units normally. Bizarre, yes, but I believe that's the only way to do it.
"A Broodlord has a BS of 0. Can he still use a nova psychic power? How about a beam psychic power?" A BS of zero just means that any shooting attacks that require a roll to hit cannot hit. Powers that hit automatically will function as normal.
"When shooting at a flyer your BS is considered 1. Does that mean a Broodlord's BS improves to 1 to shoot at a flier?" Nope! Nice try.
"Does a Tervigon with Gate of Infinity psychic power breed before teleporting, after teleporting or not at all?" Teleporting would happen at the beginning of the Movement phase, and based on the Deep Strike rules would count as movement. The Tervigon would therefore not be able to spawn before it has moved, and its rule does not allow it to spawn after it moves. Therefore, a Tervigon may not spawn termagants on a turn in which it uses Gate of Infinity.