Effective use of a coaster brake?
Stopping is relatively easy - the rearmost foot is pressing back/down on the pedal to operate the brake, the other goes on the ground. If you're used to two feet on the ground when stopped you'll need to practice stopping with one foot first. You probably need to swap anyway, so the foot on the pedals is ready to push down when you move off. It's vaguely annoying but you'll get used to it.

To shuffle the pedals around while stationary you need to be pushing gently as if you're trying to pedal forwards, while rolling the bike backwards. Again, it's annoying. When I ride a bike like this I quickly get a little system organised so that I stop, rotate the pedals forward to disengage the brake and get ready to move off, then roll back a little until the foot that's on the pedal ready to start is in the right position.

I do think you should fit a front brake of some sort just for safety. Braking with the rear wheel is less effective, especially in an emergency stop situation. Even a cheap caliper brake is better than nothing (and often that's all those bikes are set up for).