Sun CR18 is a reasonable rim choice and available in 36 holes. It isn't the lightest possible rim, but they are inexpensive, very durable, build up nicely, and are 460 grams in 700C. The CR18 works well with mid-size tires like what you are considering.
You can get much nicer tires that will also be lighter. I'm using the Compass Barlow Pass on my semi-weight weenie bike at 360 grams each. They also have much lower rolling resistance than a tire like the Kenda Kourier. A major design point for my bike was reasonable weight for putting it on the bus (I have to cross a bridge that doesn't have a bike lane to get into work).
I don't know why you'd consider 650C (571mm) for your bike. 650B (584mm) would make sense and comes in nice options for wide tires.
The electric components of my bike are a 8Fun/Bafang hub motor (SYXD-01F, 2kg), 15A controller from Grin, CA V3, and a Thun torque sensing bottom bracket. My current battery is an AllTech 36V/10AH, but it is too large and gives me a range of 60-70 miles. I plan on downsizing there.
I often ride my bike unpowered and there is no noticeable drag from the 8Fun hub when it isn't in use.
The torque assist is a huge part of making this bike work for me, so the Bafang mid-drive wouldn't be an option that I'd consider.