you can build 512 KB in this computer i have a wavy msx 2+ and it also has 64 kb ram
nut

because the turbo-r/your comp/my wavy have the same memmory controller
for example if you want 512 kb internal ram you should buy
4x256 KB because you have to install it in pairs of 2
2x256 4 bit KB = 256KB 8 bit in bank 0
2x256 4 bit KB = 256KB 8 bit in bank 1
if you cant solder at all then leave it
you should try to find a
second hand 4MB memmory mapper of msx computer club gouda.
works exelent on 3,5 and 7 MHZ