Should I do real engines or base them off of real ones?

I want to start my own fleet and model railway but I’m torn on if I should try to model real locomotives or design my own but take heavy inspiration from real ones. I have been doing lots of research and found that many steam locomotives only really had basic classifications but were then given specifications from their respective companies. I wanna do both Steam and Diesel-Electric Locomotives and I am using my own color scheme for my railway but any opinions on what I should do for the...