I haven't had issues with relays in the passed. I typically pull a bunch from the junkyard because they usually haven't been swapped out. I know all the ones I have are Omron and no issues.
If you are planning on redoing a bunch of circuits, you should consider a fuse box that contains your relays and fuses.
Waytek wire carries a few different versions. I have used 4 of the smaller boxes on 3 different projects and they work great and are completely sealed (cavity plugs, cable seals, and a lid seal).
As far as wiring goes, I typically stick to 12 awg for any power circuit (distributor, starter, etc...), 14 awg for headlights, 18 awg for relay control and marker lights. Unless you are willing to order a bunch of wire, you aren't going to have much of a choice on type of wire. Even most cheap auto parts store wire will hold up well if you protect it from abrasion, damage, and heat. I almost always using wire conduit or loom, and secure it in place.