I’ve made my own custom shoes and my advice would be to fork out the cash and buy some. From the look of your feet you would definitely benefit from custom shoes. The ones I’m riding now are the best shoes I’ve ever worn, definitely one of the best upgrades you can do.
If you are just doing it for the shoes, then pay the $2k and get some really good ones. You can justify it relative to the amount you might spend on other bike components. And it really is a performance and comfort upgrade.
If you are doing it for the enjoyment of making things, then keep going and see how far you can get. But it is not easy, there are many challenges to overcome.
Myself and 2 other composites engineers worked on the shoes for a couple of years in our spare time to get decent rideable prototypes. I can’t give you any specific tips, as our design and process are a closely guarded secret. We used flexible carbon fibre for the upper, which was very tricky to work with. Good quality thick leather would work as a substitute, how to secure it is the challenge.
One tip I can give is that the sole will need to be very strong, not just stiff. Walking in the shoes is when they are most likely to be damaged by point loads through the heal and toe. If you don’t care too much about weight then just make it a big slab of carbon and drill holes straight through for the cleat mounts. Bont used to use this method on their old A1 model shoes. They put a wood-working style star-nut on the inside of the shoes and covered it with an inner sole so it didn’t poke into the sole of the foot. To do this you may need to account for the thickness of the inner sole during your molding. That’s a proven low-tech method I’d recommend.