The whole thing about custom is that it is custom. You are starting out wanting a comuter, then switching to a cross bike, fake or real as your model, (not to mention assuming ad copy geometry is actually truthful) then wondering what those numbers are there for.

If you have done a few bikes for yourself, you should know what cockpit works for you, is comfortable, and allows you to generate power, and stay healthy. That is your seat tube angle, unless you need something weird like a triathlon bike, or whatever. From that you figure out where you need the bars to be for your reach, and the stance you will have on the bike, and so forth. And just keep going design from first principles.