Good advice above about finding a hill and testing the brakes at speeds you will be travelling. Keep in mind that speed can be addictive - I am almost 70. If your brakes are good, they should handle it. As in all things, we need to ride to the conditions and brakes are part of that. If you can go down a hill at 35 and stop confidently, then your brakes are good enough. In the wet things may be different. Rim brakes don't do so well, but you will already know what your bike's brakes are like in lots of situations.

With Bafang Mid Drive, you're going to be doing speeds up to 30mph. Very easily and often you will be doing speeds over 20mph. Take your bike out on the street, find a hill and get going that fast, you know, with a helmet and gloves and stuff. And then test your brakes and see how it feels to come to a stop. Also keep in mind you will be adding even more weight to the bike with the ebike kit, so that will also make braking worse. V-brakes can be ok if you just plan on going really slow and keeping away from traffic and other things like another biker or pedestrian. you really need to be able to stop quickly. I would recommend 4 piston hydraulic brakes to people who like to ride fast like myself. I obey the traffic rules, and i like to go 28mph. This means I am constantly bringing my bike down from 28mph to a stop frequently at every corner stop sign, etc... Even hydraulic disk brakes have a hard time doing this. All of the EMTBs you will see at the bike shop will have 4 piston hydraulic brakes on them.