If your budget is $3500usd then you can have a rocking rig.
You do not list your requirements as far as the terrain you will be riding, or if its a commuter ebike for stop and go downtown riding, any hills, cargo.
Besides that - If I were you this is what I'd do.........
Buy the MXUS XF40-45H which is 3000W direct drive (means SILENCE!) buy it straight from the manufacturer - https://mxus.en.alibaba.com/
Get the 3T or 4T and lace it into a 17" or 19" motorcycle rim which correlates in bicycle terms to 19" = 24" and 17" = 21" which slows you down a bit, that is why going with a faster wind motor, but it gives you more torque.
Buy the Adaptto controller - http://adaptto.com/Products/
with the added options. Sinewave controller means even more silence!
Buy battery and charger from EM3EV - https://em3ev.com/shop
Put all that on a used brand name bicycle - https://pinkbike.com/buysell
Stay away from the generic bicycles that are sold online, along with staying away from department store bicycles. Only buy brand name bicycles like Giant, Rocky Mountain, Specialized, Kona and the like. This is where you can save a bit of money by buying used instead of new, because you dont want to skimp on this part of the build. This is your main rig, so why buy generic shiiiiiiit when you got the money ($3200usd from your link) to spend on quality components!
Torque Arms - Throttle - Cycle Analyst - https://ebikes.ca