sanding beams in a Log Home

Hi

I have a very large sanding project I am about to undertake. It involves sanding all the beams in my log home and even some of the log wall surfaces. The beams still have a lot of dirt and preservative left on them from the construction 13 years ago! And some of the interior log surfaces have some water stains that need to be sanded out. I'm thinking that I should invest in a Fein sander with a dustless vacuum. I have a few questions for anyone here who might be able to help.

1. Should I get the 6" or the 8" sander? I assume the 6" can get into tighter spots but the 8" gets more done per hour. How should I make the decision?
2. Some of the beams are adjacent to tongue and groove wood boards that I wouldn't want to hit with the sander. How can I protect those surfaces?
3. How dustless is 'dustless'?
4. Is the Fein the best way to go?

Thanks

Greg