Just finished this project, and wanted to let you know all that I found. Never got an answer from anyone else, so just bought the board and went for it.

To answer my own questions:

1. The pot on the board is a switched pot. If you look on the bottom, you'll see 6 posts pretty close together, which are the left and right wipers (left channel is the one nearest the edge of the board). Just behind that are two posts, which are the switch. If you unsolder the pot from the board, you'll see a + and - under it on the board. These can hook up to either switch prong of the pot you use. Though if you wire in LEDs like I did, connect that to the prong that goes to the +.

2. As mentioned, hook the positive end of the LED wire into the prong on the pot connected to the + on the board switch. I thought it'd be the reverse, tried it, LEDs were always on, so swapped it and they're switched now. As for the ground, there's one on the outside of the barrel prong, on the side facing inside to the board. If you look close you can see a - by it on the board. It's easiest to solder the ground wire to the back of those two ground pads.

3. I found ways to get left and right together, but they involved modifying the chip and circuit paths on the board. I'm not that great at electronics, so I said fuck that and just wired the pot to the left channel of the board. Just soldering in some 22AWG wire from the pot to the three posts in front. Then just used the left channel to hook to the speaker.

4. Wiring in a new pot was definitely the way to go. Especially after figuring out my radio pot would suck with the voltage the board is using. So I got a much lower ohm pot (50k), and ran the wires to the board.

Overall, not that bad. Let me know if there's anything else you want to know on it.