30# to 40# is plenty for docking (absent strong winds).
Range is at the limit for getting home in a calm -- about 40min max speed, or longer, with much longer total distance, if you go slower.
No reasonably sized trolling motor will work against decent (strong) wind or against strong current.
That said, I'm using either a 36# or 40# - can't remember (probably in some old post

) and it's worked fine for my "Plan B" needs.
I'm doing better with docking under sail than under motor at this point, although for the learning curve, I did appreciate the rub-rail

.
For the final few feet (<50) a paddle is the best tool. It can be deployed from wherever you are sitting; it can be used to fend off; it can be stuck vertically and used as a brake (very useful, that). I have two on board, one on each side, so one is in reach from wherever I sit. Nowadays, mostly used to get out of the wind shadow of some buildings as boats on the ramp, to kill excessive speed when coming in (easier than a U-turn), or, conversely, to make up the difference if I didn't have enough momentum after all.
Trolling motor (nowadays) mostly used to get me through bridges and canal sections where sailing isn't possible, more rarely for docking somewhere I've not been before, and occasionally to get through an extended calm spot.