preparing tracks to send to the mastering house

Yea, that was my main problem, as the mix seemed to fall out of place when removing the compressor, I got used to mix with a compressor, as I said with really really light settings. I just should mix in lower volume yea, but I can't imagine taking the compressor off as it screws the balance :\
 
^^^^^ Well, yes. Leave it on, If your mix is going to sound wrong without it leave it there (as I said earlier - we can deal with it). Just leave a bit of headroom.

I'm just going to give you an idea for the future: if you can get a mix sounding as good as you can without adding anything to master buss, imagine what a good ME with good tools could do with it!
 
My Understanding, and im pretty sure its fairly correct is that you should Never turndown the master fader. I ALWAYS group My tracks and turn them down at the individual channel faders. Its bad Gain structure. Your Turning up a whole mix then turning it down again. You'll end up getting some slight Limiting.