Split multitrack timeline into separate 'songs' and apply individual effects, pan etc to each song?

You are obviously using track effects at present. On any given clip you can select whether it's a track or a clip effect you are applying. If you open the Effects Rack window with a clip selected, you can change the way any effects are applied to it at the top by selecting either clip or track effects. This will give you complete independence for each song, and have the added benefit of letting you put extra splits in a track, and let you apply different effects within a song if you need to.

On the basis of quite a lot of experience of syncing live music to multicamera shoots, I can tell you that by far and away the easiest way to do this is to get your audio mix sorted out first, into a final track and use this as the basis for the multicam video edit. Yes, in a way it would be great to just sync all the video and audio as recorded together and do a live mix on it, but setting it all up to work reliably could easily drive you round the bend! The other thing is that how well you can do this anyway depends upon how you've synced everything. If you've got locked timecode on all your sources then you should be able to split individual songs out, but if the audio recording is, say, clapper-synced at the start then you will lose your reference points if you edit the sound. It's always easier to get the whole thing right without cutting anything at all, and making the splits into individual songs on the final mix, after you've made it. I'll be the first to admit that this is only my take on it, but it certainly works for me, and generally saves quite a bit of edit time. And I wouldn't say that it was safe to take any of this for granted! I suppose that what it comes down to in the end is that it should be possible to run Audition and Premiere in sync with each other (I think - that was the original idea) but that's a lot of resource usage in one go - so you're going to need quite a capable machine to do it, however you look at it. And obviously you can reduce that strain if you pre-mix the audio.