The good answers have already been given.

I'm an ebiker here from another forum.

Some just want to kit-convert the cheapest safe way:
that might be SLA batteries and a cheap front hub motor.

General wisdom, and I've learned the hard way: Front motors must, must, be on steel, not alloy forks.

A torque arm is a nearly vital necessity for any ebike of any real power;
even in an accident, the D axle shaft can spread apart steel dropout lips, and wind up the cord,
breaking vital wires.

Torque arm all ebikes? As a general rule, this is best.

Rear motors offer advantages of certain sorts.
Front motors also have their good points, especially for bike-speed ebikes (not over 20mph).

Ebikes are fun and they can be very neatly done by the home builder.

They can, with the new and safe LiFePo4 batteries (heavier than Lipo), take you clear across town and back,
and you just add your 150W or whatever, however, whenever you like.

Someday here I may tell about my very special "Stealth Cruiser" conversion, nearly finished now.
It will be a ride, all right, and =no front brake=

Only angels tread where fools dare to ride (no front brake).
I live in flat territory, no hills, no need to ever panic stop.
I know how to make a coaster brake, brake pretty good.
But I will not reccomend such a stunt for others: danger!