I am a fan of batson blanks and finished an RX8 9wt for a friend. He uses it for salmon and steelhead fishing in Michigan. Personally I'd avoid a kit. It isn't too hard to get the right components (if you go batson they have pdfs on their website) primarily because I would skip the snake guides that come with the kit and get 'snake brand guides'. The feet of the universals sit wonderfully on the blank and wrap like a dream. I'm never going back
Between a 6wt and 7wt, I'd go 7wt. Doubt you'll notice a 'weight' different in the rod itself and it could help you turn over bigger flies etc. I might even do an 8wt since it would move you nicely into the salmon and steelhead category, though I'm not sure the 7wt would be a problem there.
The guy that got me into rod building is in West Michigan. He runs Proof Fly Fishing and sells components like snake brand guides and very nice cork to turn your own grip. He could probably answer some area specific questions for you if you contact him.