I'd start with Missouri Boot and Shoe or Robert Land. Mattimore Harness is right up there too. I think most would agree they're among the best makers around today. Yes, your are correct. Pegged soles cost the government more per pair than sewn soles. And, without actual documentation, I'm pretty sure sewn soles were more common.
The 137th NY performed way, way better than the 20th Maine at Gettysburg. They just didn't have a self promoting blow hard of a Col. leading them. Maybe you should look up the history of the 83rd Pennsylvania too, they make the 20th Maine look like the rookies they were.
There are some very good books out there about the fighting on Culps and Lower Culps Hill. Vincent's Brigade had nothing on those boys at the other end of the line.