One problem I had with my e-rider when it was new, was a defective battery. There are effectively five 12v batteries connected in series to give you the required 60v or so. One of these was not working properly, so I only got the sort of mileage you’re talking about. If you can, check the voltage on each one, maybe with a light load, such as using the headlight.
Regarding the headlight, I have an issue with this whereby the speedo is not quite straight and prevents the headlamp being set in a horizontal position. See the post from PaulIOM above, which I’m going to try.
I’ll leave someone better qualified to answer the question about the brake light, although I assume the brakes are adjusted correctly.