Choose cells from any of the major reputable matchers. You will find that alot of the battery companies get their packs done from smc and then have their own company shrink wrap on them. Nothing wrong with this just know that everyone says their cells are the best but all come from the same distributor whether they are matched from them or not.
I personally use smc's. Have used local matchers a few times but have ultimately gone back to smc.
On building, score the ends of the cells and with a good hot iron with a broad chisel tip. You shouldn't need more then a second or two of contact to make your solder joint. I use a deans jig. A little flux on the cell and bars, tin them all. Use the pressure plate with the jig and solder them up.