This was just a trial fit,I was curious if my 3.5" spacing was going to fit in the real world. Good thing I tried it, no go!
When I do it for real, I'll space them all out, put a couple of screws in them and then move up the table for the next set. The first three sections of track will be perfectly straight, when you get to the right hand side here, those will have some bends to mate up with all the switches.
Track spacing is simple enough on straight track but less so on curves. In John ArmStrong's TRACK PLANNING FOR REALISTIC OPERATION, he proposes that every layout builder create a table of standards for their layout and he give the formula or framework for each measurement--like distance between tracks under different circumstances. Creating that table was a valuable exercise for me. And it saved me from many mistakes. Worth your time.
Curves here in the freight yard will be less critical than on operating tracks. Most of the curved sections will not be operated at the same time. Also, the intent of the yard is mostly freight cars. I won't try to park anything that doesn't fit in here.
As far as creating a table of standards, I think that ship has sailed for me, the track laying is done for the main platform. Whatever mistakes I mad (I'm sure there's one or two), I'll have to either live with or fix. One of the reasons for not rushing things like ballast is to get enough running to see if there are things that have to change before chiseling stuff in stone.