Re: Question on bus levels as impacted by individual track levels.
99 times out of 100, scook's answer is correct; just lower the bus input gain and you're good.
However, it's that 1 time out of 100 when it's not the right solution that'll bite you. Things will just sound bad and you won't know why. Some plugins don't handle signals > 0 dB properly, so it's good practice to just make a habit of keeping track levels low enough that you're out of the red when they're summed. Faced with your scenario, I would make a quick group of the tracks going into that bus, and lower them all by 6 dB. Even though it's a hassle, perhaps not worth the effort, it's just good practice.
It's like making a habit of always using your turn signals, even when you don't see any other cars around. 99 times out of a hundred, not signalling won't be a problem. It's that 1 time out of a hundred when you get blindsided by a garbage truck - that's when you make signalling an automatic habit.
All else is in doubt, so this is the truth I cling to. My Stuff