Putting a thin piece of MDF/plywood with rounded undersides to the edges on the bottom of the bag would also help with both wear and bowing.
Copper rivets (copper pin with a washer - the pin end is peened over to trap the washer) are more durable, but require some special tooling to install. “Speedy” rivets (a pin with a hollow cap - the cap is hammered down onto the end of the pin which flares into the cap) are probably good enough for stress points. We have the tools for speedy rivets in CA. Pop rivets are also an option, albeit an ugly one.
Diamond lacing chisels make nice holes easier than using an awl to poke a hole for each stitch. If you have CAD skills, you can also design/cut the parts on the laser and use 0.05" holes (or rhombuses maxing 0.05") to precut the stitching holes. I’ve used this to good effect making knife sheaths, and is a lot easier than holes-as-you-go, but takes planning for all the alignment to come out right. I (and several others) can show you how to saddle stitch the leather. This makes for a much more durable seam than using a sewing awl/speedystitcher which creates a chain stitch which can unravel more easily if damaged
re: leather selection
The example you show in the first couple of pics looks like saddle leather or harness leather (7-8oz, perhaps thicker). In modern parlance, a leather “ounce” is 1/64" thick so 8 oz leather would be about 8/64" (or 1/8") thick. You’ll probably want a “double shoulder” sized piece, or even a “side” if you want to cut a 1 or 3 piece pattern.
I’d recommend making a mockup of the main bag template (flat) and take it to Tandy so you can hold the pattern against the hide you might buy to insure a) it fits and b) it avoids any flaws possibly present in the specific hide. You can often buy a cheaper grade of hide and work around any holes present if you plan ahead.
The version @frank_lima referenced is 11Lx8.5Wx8.5 tall. A 1-piece pattern would end up about 27"x30" roughed out for the basic box, before pockets, dividers, etc.
I’d recommend vegtan leather with oil/wax added. Some cheap chrome-tanned leathers can be corrosive to metal tools if chromium salts are not completely neutralized. Brown/tan leathers are typically veg-tan based. Chrome-tanned leather is gray on the back but typically drum-dyed another color.
Buffalo is a nice strong leather with a pebbly texture which would look good on a bag like this.
Options (these are both “sides” with 10+ sq ft of leather - probably enough to make 2, possibly 3 bags):
Veg-tan saddle skirting
The water buffalo has been waterproofed with waxes and oils. The vegtan would need treatment to protect from water/spills, but can be tooled/stamped
Unless on sale, finding someone with an “elite” Tandy membership would save you some $$$.