Interesting concept you got going on there. To do a traditional lace the spokes would be radial which is not the best for strength, I can see why you want to do it your way. You will be bolting your "spoke" plate onto the flange of your QS motor then having a "L" on that plate for the rim mount. Maybe make it a 2 piece?
Most motorcycle rims I see have bulges in them to help with spoke alignment.
Since you already have the motor, just get the rim and measure its E.R.D. then go to Justins www.ebikes.ca
Spoke Calculator. We MXUS guys have it quite easy as the motors specs are already in the pull down menu, but its easy to measure and input the QS numbers.
You could just go ahead and try the radially laced concept with some cheap ebay generic spokes of say 12G straight, or if you can find double butted 12-13G. Give it a whirl and if you dig it, then get the Sapim 12G.
What you do not want to happen when you build your spoke plate is the flange on the motor to break, because then you are pooched.
There are two things to watch out for with radial wheels. Because the nipples point straight inward from the rim, they can turn more easily in most rims than when they are bent to a slight angle by a semi-tangent spoke pattern. This ease of turning increases the risk of their unscrewing themselves on the road. To prevent this, nipples on radial wheels should not be lubricated, and it is a good idea to use a spoke adhesive such as Wheelsmith Spoke Prep or one of the milder flavors of Loctite ® on them. (Or, if a rim does not have recessed spoke holes, the rim tape and air pressure in the inner tube will keep the spokes from turning -- at least with a high-pressure tire).
The other potential problem with radial wheels is that the spokes, trailing straight outward on the hub flange, can possibly rip the outer edge of the flange right off along the line of the spoke holes. This is most likely to happen with small-flange, 36 hole hubs, because there is less metal between the spoke holes. If a used hub is re-laced radially, the notches left by the old spokes can act as stress risers, further weakening the flange.
Many hub manufacturers specifically recommend against radial spoking for this reason, and will not honor warranties on hubs that have been spoked radially.
Some folks will say that no bicycle wheels should be radially spoked for this reason, so do this at your own risk. In my experience, it's generally OK with good-quality hubs that have forged shells.
You can use Boiled Linseed Oil, or Phils Oil.