So my first career was as a historical and theatrical costumer. I've done some basic cobbling and can make my own moccasins. It's awesome, and fun, and if you have strong sewing skills you can make some really nice moccasins, but a) there are a LOT of skills involved. I can copy a full Elizabethan Court Dress no-sweat, so I am by no means a sewing rookie... but my first couple of tries at making my own shoes looked like I was a kid in a sandbox. Working with leather and dealing with grain and thickness and the specific differences in hides and dye lots and parts of the hide takes serious experience and skill before you'll be good at it... and b) the costs of materials are substantial. You'll need leatherworking tools (which are NOT the same as sewing tools! You need awls, leather scrapers to bevel the leather for seams, and specific chisel-point needles and punches to go through multiple layers of heavy leather), specific glues, heavy-duty leather, and probably, if you're not hand-sewing, a new sewing machine with gears and a motor strong enough to tackle shoe leather.
My experience was that it's really not something that works as a side hustle unless you're deeply into the RenFaire, re-enactor or SCA crowd (I was, and was branching out of a successful costume and corsetry business) and even then you're competing against much larger and more experienced makers who have economies of size and talent. These are literally the "boots that cost more than your car" boots... so a lot of people who are in the market for them aren't as price sensitive as you might think because it is a once-in-a-lifetime status-symbol purchase for them.
Anyway, I've mostly moved on to house slippers for friends and family, but when I was working in leather I bought the majority of my supplies from Tandy Leatherworking online, working in bull leather with deerhide for decoration, and got the soles and insoles that I needed off e-bay where there are plenty of Vibram options. There is a lot of information on how to put moccs together online, although most of it is geared either toward turnshoes (medieval) or buckskins, so use your imagination. :)