Older bikes are great, but you really need to turn your own wrenches, have a stash of old parts, or have a good co-op close by.
I still have a freewheel bike, but I was fortunate to get a few Sachs Aris freewheels before they went to triple digits. When I see a chainring I can use one day, at a good price, I get it and pack it away.
You can find great parts at co-ops, but you do need to know what you are looking for and at.
If this is what you want, go for it. Old bikes are a lot of fun. Figuring out what will work and mix-n-matching non-spec stuff is really rewarding.
If you have to take a 40/50 year old bike into a shop it can sometimes be frustrating.
John