TMS9918 expects 8x 4 KiB TMS4116 as external VRAM, which is DRAM with negative voltage bias rail, but there's a neat hack I found to make it use a generic 32 KiB SRAM with some register chips. I might try to convert the YPbPr component video output to RGB VGA at some point.
I'll need to manually implement I/O logic for stuff like bank switching to let Z80 efficiently use the whole RAM whilst being able to access the ROM.
Also TMS9918 and AY-3-8910 naturally have much lower clock speeds, so I'll need to learn to do clock stretching.