I'd like to say that I could answer all your questions, but unfortunately it takes a long time to learn it all. I wouldn't recommend buying leather on Tandy's site, you should see the hides you're buying in person to check for defects, scars, bug bites, wrinkling, etc. Every hide is different. In the case of the belt, I had to dig through a stack of 30 belly hides to find two that my patterns would fit on and weren't flawed anywhere I needed. I can repeat from before though that my gauntlets are made from 7-8 oz. hides and the belt is made mostly from 10-11 oz. belly hides. The straps are made from 2 oz, as I didn't have anything in a 3 in my scrap pile. I'd recommend going to your local Tandy if you have one and asking if they teach classes. Get the full starter kit, take the class, and keep going. What the class didn't teach me much of was proper edge finishing, I learned that from my boss when I did this for a living. My process is this:
Cut the piece into the right shape. Use and edger (cuts the edge off at an angle) on the back, taking off a fair amount (hard to define, but don't go more than 45% of the way through the hide). Flip the piece and use the edger on the front, only taking off a very small bit of the edge, and holding it very steady so that you don't make the line wavy. This can take a LOT of practice to get right. Get the edge of the hide damp and use a slicker, the wood one works best, to round the edge. Then for most of my pieces I use an edge groover, which puts a line along the edge. Personal preference. After the hide dries, you can dye it, put satin or super shene on it to seal in the dye (in the case of the Altair costume, use A LOT so it doesn't rub off on the white fabric. I didn't dye the backs of these pieces for that reason. After it's dry again, rub some wax on the edges and use the slicker again, moving it very fast and applying light pressure to heat up the wax so it seeps into the imperfections and makes the edge smooth.
I hope all that can help you a bit. I do have to say though that getting into leather work is a huge investment. I think my tool kit at this point cost about $500, and that was with business pricing for most of the pieces.
