I use anti-seize for anything stainless to keep the threads from galling, but I don't rely on it exclusively to separate metals. I like to cut my favorite pond liner washers for lots of things and also make washers out of heavier plastic as well. I always have trouble getting the washers I want so that's why I cut my own.
Dudes, most hot rods out there violate EPA policy. Private citizens can do stuff. Motor vehicle registrations are a state issue. EPA regulations are aimed at commercial enterprises, and the enforcement power comes from the government's right to regulate interstate commerce. Many states even have procedures for documenting your re-power on the state-issued title. Sometimes states actually decide things related to this, like a few years back when Wisconsin or Minnesota or some place decided to stop issuing title docs for Pinzgauers, but that is pretty unusual. I'm not a lawyer, and my advice is worth nothing, but you all can all keep building hot rods in relative confidence and peace of mind.
Are you not using mcmaster.com? Hardware store prices for fasteners are crazy. For your nice finish body bolts in stainless, I think Nakatanenga's kit is by far the best. Otherwise, you just need to get good at speccing and ordering fasteners in quantities from McMaster-Carr or Fastenal. There aren't that many sizes really, a whole bunch of M8x25 and M6x20 and the a smattering of longer M10s and a few big long M12s back on the rear crossmember (that's admittedly oversimplifying it, but it's mainly just M6, M8, M10, and a few M12's in a variety of lengths). You're going to try to be comprehensive about it, but until you have extra bolts sitting around, you just have to get accustomed to the fact that some days your work will stop while you drive down to Fastenal or place another McMaster order
I only have been to Fastenal stores, never online. I only buy bulk fasteners for generic applications like body bolts, chassis fittings etc. if the part rotates, flexes, or moves in any way, I buy original fasteners.