First off pick your frame size- the difference between handlebar stem & seat post. Short people need 16-18", medium 18-20", tall 21-22". Courts reviews will tell you this, as should the bike website. Some brands only come in medium. Others the short ones are special order, you pay before you try the bike.
Then pick wheel size. I'm short but like 26" wheels with 2" tires for bad pavement. Taller people can take 700 cm or taller wheels. 20" wheels carry well up an apartment stair but are vile through a pothole.
Power all the time, a mid drive can work and with torque sensor, feels very natural. They wear out chains. Pedal yourself sometimes, a geared hub motor or a yamaha mid drive, you don't want drag.
I like the hub motors, when something wears out any brand replacement will fit the dropout (fork) of a standard sized bike. DD hub motors are cheapest, longest life, and work okay in cities, but hog watt hours on the many hills like I ride. DD hubs are heavy to carry or lift. Geared hubs may have 3000 or 5000 miles life, but are very cheap. I ride one, about 8 lbs and hardly noticeable locked to a downtown pole.
I have mechanical disk brakes and they are fine over the 80 or so hills I ride on my commute. Need adjusting about once a year (2000 miles). Hydraulic disks are for the really high speed down really long grades, not worth the maintenance bother (bleeding) & cost imho. I stopped in 20' from 25 mph last week with my tektro mechanicals. I feel rim brakes are **** in the rain and ran into a car with those after I stopped at a 4 way stop sign and she didn't.
Extremely high speeds (20 up) you want full suspension. 8-15 mph like I ride, 2" tires smooth out the bumps enough. Extremely bad city pavement, maybe suspension is worth the cost. Seat post spring is about $100 if you buy a front suspension only bike. Suspension parts may not be available a few years after you buy, requiring a new bike.
Bargain brands are magnum, juiced, M2s. Rad is cheap but electronic order only. Full service brands are pedego & trek. Bigger batteries run the costs up, at your range 10 AH would be plenty.
Best in the rain is arroyo probably, they are made in Netherlands where it rains all the time. It rains a lot here & I oil steel parts on my bike every 2 weeks. Cables have been replaced with stainless with plastic tubes.
Fenders are available but headlights & taillights, you can save a lot of money by buying aftermarket from modernbike or niagara ( just changed name, I forget new one). Wears out, no maintenance hassle, throw away & buy new. Mine use a MicroUSB charger, about every 5 hours of use.
If you really want to try a lot of types, shop in LA, SF, Chicagoland, East Coast (not NYC where ebikes have been illegal until recently). MA has a low power limit, I wouldn't shop there unless I lived there.
Have fun shopping.
