Location of water pressure regulator
Should make no practical difference. I'd also suggest an accessible "secondary" shutoff if your "main" is a pain to get to. When it needs to be shut off NOW, you don't want to be facing a long crawl in a nasty hole before you can get that done. Plumbing in some gauges so you can see where it's set and if it's actually doing its job is also helpful in the long run, IMHO.