You're going to get a LOT of opinions on this. Most mount theirs in the tail area under the seat because there is plenty of room back there. Some mount them behind the headlight, but that can be a pain to get to if you need to add a farkle or change a fuse. I mounted mine in the storage box on the left side of the fairing. Of course this meant that I had to drill several holes in the bottom and sides of the box, but I like having it there because it's easy to get to and makes adding farkles easier. I also like it because most farkles are on the front of the bike, not the back, so I don't have as far to run my wires. Nice, clean, and easy. Unfortunately I didn't take any pics during the install, so I can't show you much.
As for the relay, I put mine to the left of the battery and triggered it off the accessory connector that's stashed on the right side of the battery. All in all it makes for a clean and relatively easy install.