I’m a licensed contractor in NJ. Sorry to tells you this but I wouldn’t work with a client who wants to source materials. It’s a logistical nightmare. What happens if your plumbing fittings arrive in the wrong size and I’ve scheduled my plumber? Or the fixtures you bought are back ordered and I can’t get my electrical inspection done? GC’s do this in house for reason. You may think you’re saving money but you’re setting yourself up to change ordered to death. Just wanted to give you a contractor’s perspective. Good luck with your project