To the best of my knowledge, as Mike would be the better person to ask. He is pretty good at getting back to people, considering, as I get the impression that he is swamped with emails and PMs, so I try my best to not bug him.
1. With the LR kit, you can use any bottom bracket and crank that you like. You will, be, I think, limited to a single chainring in the front, as you have 2 separate chain runs. I am planning to run with a single chainring up front. If I need more gear range, I will purchase a Patterson or Schlumph drive for the front.
2. As to the Q-factor, I have no idea. I am not sure if Mike knows yet, as he just got the mounting plates in for the BD drive. I assume he is working now (or soon) on installing the drive to my bike. Once that is done, we will know more about the chainline. It all depends on where he puts that jackshaft.
3. "Overkill." Who knows. Depends on your needs. It is overkill for what I will use it for on a daily basis (a commuter). But, I will also be bikepacking with this rig and possibly pulling a gross of 500-600 lbs (tons of camping gear, plus a trailer for my son, using it to haul firewood, etc). Because it is roughly the same pricepoint as the Stokemonkey and vastly more powerful, I think your decision should be between the LR and the Bafang.
Advantages of LR kit over Stokemonkey:
1. ~10x more power, if wanted.
2. Can pedal or not, your choice.
3. Very easy and cheap to change the first drive ratio (easy to adjust that cruising pedal cadence)
4. Should be easy to self-service when needed.
The downsides are, perhaps:
1. It is untested (Stokemonkey has been used for years and is, I think, very reliable).
2. I have no idea what the all-up-weight will be of the LR kit, but it appears heavier than the SM.
3. How waterproof is it? Hard to say (untested), but it is mounted in a spot that is largely protected from rain by the rider, especially if I wear rain gear.
4. Resellable? This drive is ONLY for the Big Dummy. If you decide to sell it later, you have to find a BD owner who wants is, or sell the whole bike. The Bafang is easy to uninstall and sell, and so is the original BB LR kit. The SM will be hard to sell as well, as it is only mountable on a few bikes.