Thanks, guys. To elaborate, I had installed a relay when I installed a single-beam HID setup. The high initial draw of HID is allegedly not good for switches. But with the new wiring harness, I'll be going back to H4. (Not that the HID was unsatisfactory as a light...I just didn't want to face a problem with it overseas and be unable to get a replacement lamp. H4 is always easy to find.)
There's a lot of testimony online about relays making lights brighter and decreasing wear on switches, etc., but when I looked at the schematics I have drawn for my own bike, it just didn't really seem to be accomplishing much in practical terms in my case. Maybe a connection or two less, but I didn't see how that would really result in any major loss of output from the lamp; plus, it added a bunch more potential points of failure. Given that my bike's likely to see harsh environments and over-sea transportation, keeping things to a minimum really seems like the best idea.
In my case, the wires are 16ga, which according to my chart here should be overkill to carry the required current. I think I will fuse at 10 amps just to be cautious.
Connectors are all going to be high-quality automotive stuff; I'm actually planning on using Weatherpack for my exterior block connectors if I can stomach the price of the crimper. Got a few other sealed options I'm also considering which may be compatible with the crimper and dies I have, too. Switch is a cheapo generic bar switch (hi/lo/off and horn only) but it's super-simple and should be easy to clean and/or replace if required.
Thanks again for your input and reassurance.