Not sure if sanding is a good idea. Since you're not sure if its leather or vinyl maybe some polish will darken up the scratches. I would try it first before doing anything else.
Since they're steel they may rust coming over from Hong Kong. They should clean up though. Also you will be waiting a couple to 3 weeks for delivery. I've ordered from Etsy in Hong Kong and it's not fast shipping.
Big job and lots of leather!! My only concern is the looseness of the leather. You are brave for such a big project. I've done upholstery and it's not my favorite job!
I've heard a few negatives of the Springfield interiors...how do you think the quality is? If I remember right I heard crooked stitching. Great looking wallet by the way!
What about incorporating a magnetic closer? No visible snap and something I've not seen done on a biker wallet. I'll be interested to see what you come up with.