Newbie needs help ...

I’ve never ever understood the appeal of those giant twenty inch wheels on older cars that weren’t designed for them. They make the car look ridiculous. It’s a very wise move removing them from an otherwise great looking car. Your car would thank you if it could.

Depends on the car, the build, the use, the tire on that wheel, etc.

On a 67-69 dart I would not go 20" either but to blancket all cars older cars like that, no.

Also, while maybe 20's aren't he ideal look for many, i've had classic cars come with 13's and 14's. Going up some from there with a decent aspect ratio yields a nice look and good function.