[Greenbuilding] Door frames and gaskets

[bill.allen at verizon.net]

I am finishing up a small outbuilding that will be conditioned (living space) all year in NE PA. Since it's small, the entrance door is an unusually large percentage of the wall surface area. I plan to build my own, insulated door but I have the following 2 questions and would really appreciate any info/comments:

1) A traditional door frame would be the worst thermal bridge offender in the whole project. Is there a construction technique that would eliminate this?

2) Local box stores offer many types of gaskets/sealers for all 4 sides of a door.  What are folks using to get the best seal?

Thanks for your consideration.

Bill