After having a 500W Golden Motor direct drive hub motor on a Recumbent trike, with a 36V 10A.hr battery, with its range reducing from 35 km to 15 to 20 km, if I went up a slope greater than 3%, I would STRONGLY recommend a Mid drive motor for hill climbing, (500W, but derated to 250w) to replace the crank, so that the power goes through the
9 speed (11-34T)rear cluster (for greater chain strength!).
It will be a 9 speed electric bike, instead of a Single speed electric bike!
Can you remember how hard it was climbing a hill on a single speed, heavy steel bike with a back pedal rear brake, that would not work every time!!!!
http://wooshbikes.co.uk/?motorcharts
A permanent magnet motor is ONLY efficient from 80% to 100% of its maximum speed.
Look at the Santana geared hub motor curve with the blue bottom line being flat ground, and
the current draw at 15 mph is 400 watts, compared to 100 watts at 16.5 mph!!!
With a Bafang BBS-001 36V 500W motor with INBUILT 25 amps controller, controlled to 15 A, then you select the gear for the required speed and 78 to 80 cadence(max motor efficiency speed), and use the pedal assist level (3 to 9 levels) for the amount of electric assistance required.
The Bafang BBS-002 48V 750W motor has a 127 rpm max speed, and the BBS-HD 48V 1500W has a 170 rpm max speed, so neither of these can be pedal assisted and are ONLY for Electric MTB Off road ALL electric use!
If using 26" or 700c wheels, I would recommend the Lekkie 36T offset wide narrow chainring(so max powered speed is 30 kph(20mph), std cranks, std throttle, stb brake levers(to stop motor), Gear sensor (to stop motor during a gear change), Egg small color display, and 36V 17 A.Hr battery from California Ebike for $1387.
https://california-ebike.com/shop/bafang-bbs02-mid-drive-custom-build-bundle/
And a bafang BB tool BPT-1 ($35), and a programming cable ($30)
California Ebike has the best reputation on the West coast for the E MTB groups, and rebuilds/upgrades and lots of spares, for Bafangs and Hub motors!