Coming from a motorcycle background I'd recommend Excel, DID or Sun rims. They are all available in 2.15-19" from many places. I personally like Excel and have had excellent luck with them. They come in many colors. For an ebike I'd go with a Takasago version they're the most common. If you don't care about an exact color you can usually get them for $125 on eBay or close to that. Often times off colors sell for a big discount. I've bought them from FasterUSA too, brand new.
For spokes, I'd also use Buchanans. I just did this with a similar motor and rim to you. I'm using the QS205 and a 19-1.4" rims. Because Excel doesn't make them that skinny, and I wanted gold rims, I went with Pro Wheel. They look sturdy enough. My spoke length for the rear ended up being 128mm but def measure first. I used 9ga on the rear in a 1 cross, stainless spoke with brass nipples. I had to spec 0.250" nipples to fit the Pro Wheel. I paid about $110 if I remember for 36 spokes and nipples. Yes it's a little high but I've bought from them before and it's worth it for the quality and service. They also sell the rims if you want a one stop shop but you can do better on those by shopping around. They are super easy to deal with and they're entire business is manufacturing spokes. I have about 6 wheels they have laced up for me and they have all seen hard use, zero issues.
For my front hub, I'm using a Hope Pro4 36H with the same rim. I went with 12g after numerous ebike gurus told me that my plan of using 9g was not a good one. I had already drilled another hub so I chocked it up as a lesson and bought a new hub. For those spokes i went with Sapim Leader in 12g and I think the length I calculated was 222mm but I can't remember exactly. I just ordered those a few days ago. They were pretty cheap in comparison on eBay from some bike guy in Chicago. I plan on a 3 cross pattern. Will do the lacing and truing myself on a stand I built years ago.
Hope that helps, I'm not an expert on ebikes by any stretch but I do know the motorcycle rims and spokes thing pretty well.
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