The hardware developer did a small redesign of the cart because there were some reliability issues. Now I am waiting for a second run of cart prototypes and hope that the issue is fixed and to post a picture of it soon.
Depends on your attitude, time and budget. It may range from reading in the net to getting a formal education. My personal preference is reading books. This link seems to have a few good ones: https://www.programiz.com/c-programming
Keep an eye at this forum every now and then in a few months there might be much better ways to develop for the thing. Learn C if you don't know it. And every knowledge of the low level programming you get meanwhile won't go for a waste!
Guys, I'm more worried about the thing happening at all. If it doesn't, then there will be nothing available, hence price would be infinite high! Now that the price question is out of the way here are some good news. My friend made a decision for the flasher casing. It looks very good in my opinion....
On the flash cart - I've met with my friend last weekend. He is committed to make it happen within the next weeks which is great news. Now he is ordering the parts for the flasher and the cart, and is finishing the design of the flasher PCB. Well keep you posted on the development.