Remember your compatability. You'll need 130mm rear spacing if you wanna run more gears and brifters. But 126 will work, just more of a pain. Try to get downtube shifter bosses so you can run cable stoppers on them. For stem, a new threadless fork on an older bike (1") is still possible. Much easier to play around stem length with newer non-quill stems.
Most important: have fun with what you are doing!