I like the ancient colours woven by Lochcarron too - not many chaps like the predominant colour of 'orange' that is typically seen in many of the red-based, 'ancient' coloured tartans, but I do.
I'm with you on that, Kyle. Sadly, none of my clan tartan variations have a red base to them. I'm thinking about a future kilt in a non-clan tartan that I can get done in that lovely ancient red colour, just because I like it.

As to the original question, I think any of the ancient/weathered tartans would look great with brown straps. Modern colours and dress tartans are probably best with black straps. You might also want to consider, though, if you'll ever wear any of these in a more formal setting where you'd be pairing them with black leather shoes, sporran, etc. It might be a bit of a fashion faux pas to have a brown strap visible (though most folks probably wouldn't notice or care).

As for the number of straps, I'm a solid three-strap fellow. I like to see the third strap on the right side, and I think it helps the kilt construction in conforming to one's body shape, even if it's buckled loosely. But that's just me.