On the SDRAM... You'll be getting a properly registered/buffered module, I hope? Kingston ValueRAM sold here in the US is the usual generic stuff, though they do offer 'custom' modules for, say, older server hardware that might be compatible?
I don't think the GeForce would have trouble under PPCBoot/U-Boot (unless the nVidia BIOS is odder than ATI's)... have you asked Eyetech or the AmigaOne Yahoo! group before going shopping?
