Kapusta

Assuming you plan to buy the frame from an authorized Trek dealer, you questions are best answered by Trek, not BF.

I would THINK that if the frame cracks within the warranty period, it would be replaced or fixed. But again, ask Trek. Also check the details of HOW the warranty is handled. With companies like Santa Cruz and Turner, problems are resolved pretty directly. My experience with Marin was that the process was so prohibitively long and expensive for me that the warranty was essentially worthless..

Just be sure that the parts you have will play nicely with the frame. In particular, are the axle standards compatible, and if not, are the wheels convertible. Also double check bottom bracket compatibility and see what may be needed to adapt if need be.