I'm a pretty amateur leather worker in terms of this site, but I am a professional bookbinder/conservator, and I just want to add that it is really important to remember the grain direction of the paper and the wood (everything needs to run parallel to the spine), otherwise you will get major warping. Depending on how many signatures you want to include, I'd consider using 1/4" board. 1/8" will warp pretty easily with leather attached to it, though I understand if it's a thin book, 1/4" can look too hefty. You'll also want to sew the text block directly to the boards, as typically glue alone won't hold up over time.
I'll try to dig up a few coptic or longstitch pdfs I have floating around and upload them here when I get home from work. What do you mean "extra leather around the edges?"