I came very close to this when I started three years ago.
I was trying to read everything, plan everything, draw everything -- to the point that I almost decided I didn't want to do it.
Then I decided I was just going to jump in.
I made everything modern day, but I also have some trains that are from the 1950s.
Some modelers would not like that, but it doesn't matter to me. I like it.
If I had started 50 years ago, I probably would be on my 4th or 5th layout, and maybe the era and location would be set.
But in my case, I was old and retired when I started, so I don't have the luxury of time to do things, then start over with certain things that fit.