Thanks for all the insight fellas. Any day I get a working job successfully completed on the X5 is a good one. The lights are working, controlled by the switch I added to the ashtray cig lighter socket before. The switch is powered with the ignition in position one, and unpowered with the ignition fully off, which is nice.
Since I had already run a power wire for the switched relay under the dash from the ash tray to the cigarette socket in the pax footwell, I decided to first try to move it to the flashlight charger power, behind the glove box. The kick panel(s) came out quickly and from there it’s easy to reach behind and unplug the charger socket. A quick check for power (it’s powered at ignition position 1) and then the splice. I fumbled for a bit trying to plug it back in, but eventually got it. One more voltage check at where the wire comes out at the ash tray and I verified 11.8 V (engine off, key position 1).
Splice circled:

Next up was to route the load end of the provided harness to the KC lights and then pull the other end of the harness through the firewall. The plug end went under the oil filter bracket and behind the left front light, secured with a couple of zip ties to convenient wire bundles. The plug on the lights is just long enough to extend into the bumper a bit via the cooling slot, where it plugged into the harness.
Initially I wanted to keep the relay and load power fuse/wiring on the cabin side of the cowl, with the brake booster, etc., because it is a bit messy. However, I decided eventually putting it all under the hood on the engine side would be less moisture prone. The relay mounted with a self tapping screw and the fuse assembly mounted to a convenient threaded stud on the strut tower. Not sure what it is for, but it has a plastic nut on it.

I pulled the switch wires through the firewall by taping it to the old light wiring and gently pulling it all the way through and out of the cigarette lighter hole, to meet the relay power wire I had run initially. The harness from KC already had spade connectors for the switch on it, and I put one on the relay hot wire I ran.

Way too much wire included on this side of the relay for the switch wiring:

I chopped it down to an approximate length, and spliced it back together with some crimped in-line wire splice pieces.
After that I cleaned up under the hood and drivers side footwell with cloth electrical tape and a few zips, tested it successfully, and buttoned the beast up.
I’m excited to see how bright these things are, and get them aimed properly. They are very focused it seems. If I lowered my head a few more inches in the below pic, they become blindingly bright.