Best donor frame to build an electric bike & getting started

Bullfrog said:
Disc Brake Advantages:
Disc brakes offer greater stopping power, which can be helpful on long descents.

Nope. Good rim brakes can be every bit as strong as the strongest discs. And lousy disc brakes can be as bad as the worst rim brakes. Maximum braking power is always limited by the bike's weight distribution and available tire adhesion, and both rim and disc brakes can easily exceed this maximum limit. Maximum continuous braking power, like on a long descent, is higher for rim brakes, because their rotor (the rim) has more thermal capacity and surface area to discharge heat.

Disc brakes allow for more precise braking, making wheel lockup less likely.

This is often repeated, but the opposite is true. Discs are more likely to give you stronger braking than intended with a light pull at the lever. That's more likely to get you in trouble than any other braking behavior.

Disc brakes work better than rim brakes in wet weather.

Disc brakes get wet because they are on the outside of the bike. When they do, it often makes them noisy and changes their lever response, just like rim brakes. Using appropriate pads can make rim brakes totally acceptable in wet conditions.

Changing rotor sizes allows you to adjust how much braking power you want.

There are more and easier ways to adjust braking response with rim brakes than with discs, so this isn't really an advantage. It's just a quality that they share. Lever pull ratio, lever blade length, pad friction coefficient, straddle cable angle, rim surface finish, cable housing type, spring loaded brake noodles, etc.

As for real disc brake advantages you didn't specify:

Discs allow you to use any rim, including those that don't have braking surfaces. Such rims are becoming more common with the increasing popularity of discs.

Discs allow the rim to be substantially out of true without causing problems.

Discs can make removing and reinstalling the wheel a little bit simpler, especially compared to rim brakes that don't have a cable tension release.

As long as the rotor remains flat and true, discs tend to be very simple to make routine adjustments. It's when doing more serious repairs and maintenance that they become a headache.
Rim brakes can be fine. But when you rack up lots of miles, I came to appreciate a bit longer intervals between adjustments and pad replacements. But both always stopped fine for me, riding mostly less than 35 mph.

So that cruiser got disc, front and rear. Wet or mud not an issue here in the desert, very often. I just like it that I don't have to fiddle with em much. BB5 copy calipers btw, nothing fancy.