You are correct. I am looking to build somewhat of a retro scrambler style bike rather than a more modern style long travel bike. I completely agree with you about aesthetics. I would prefer an 18-19 combo for the vintage flare. That said I plan to ride the bejesus out of this thing and it's been my experience that when on the road it is easier to find 21in front DS tires. The other issue for me is cost. I was able to find a front wheel to match my fork and it only ran me $50.00 with a disc and brand new wheel bearings.
The suspension issue is my biggest concern right now. 6in does seem to be the max for the rear with the stock shock mounts. Right now my fork is has 9in of travel and I'm not sure that I want such an unbalanced travel range. Still kicking it around though. I know others have short travel rears with long travel front ends and seem to really be able to get the job done (Sanjoh's dirt ninja comes to mind). The key to keep it in check will be the shock quality. This bike will more than likely have a bit more "heft" than a Dirt Ninja.
I hope to update the thread soon. The holidays are kicking my ass at work right now which is a good thing because I've got parts to buy....