This looks like a great project, a fun toy to play with.
However, stating that:
> I've always wanted a low-cost portable FPGA with video output to make my own CPU, but there isn't any on the market.
is definitely not true: one can buy Sipeed's Tang Nano boards for $25+ on Amazon (or less if one needs fewer than 20k LUTs).
Oh that's nice, how come I never saw those!
The Gowin chips are quite interesting - they have RAM built in to the FPGA itself. It's SDRAM in the case of the Tang Nano 20k. It's a 32-bit wide RAM, but unfortunately only 8 megabytes, which is a bit limiting. The FPGA's clocking is a bit limited, too. (For that reason, there's an extra clock generator on the Tang Nano 20k.)