This doesn't look right to me. Cartridge connector ~CS is not a chip select signal for a ROM, and if you use it like that, you can cause hardware damage because there will be bus contention with the work RAM chip.A0-A15 -> A0-A15 (obviously)
CE -> CS (Pin 5 of edge connector)
But since you haven't yet booted an actual game, I think you should be ok because I don't think the boot ROM reads work RAM.
Also, if you don't have a mapper chip, you can only have 32 kB of ROM which means A0-A14 pins can be connected, but A15 should be permanently tied to VCC or GND.
So this is not a correct assumption:
You will never be able to have a 64 kB game without a mapper chip / banking method of some sort.As far as I can tell I should be able to load a 64KB game off a W27C512 without issue
This reply to has some more information:
And here's a schematic for a 32 kB cart for reference: (note that the flash chip is 1Mbit and unused address pins are tied to VCC!)
https://github.com/Gekkio/gb-hardware/b ... T32K-A.pdf