The only thing missing from this motor is the ignitor which will be fed thru the nozzle, and thru all the grains all the way to the top of the last grain.
Ignition occurs at the end opposite of the nozzle. The fire travels down thru the center of the grains and out the nozzle. The fuel grains burn from the inside out. The holes in the center are a requirement. This is true for almost all solid rocket motors.
I'll share launch videos for sure
As for paint... The small amount of weight added, and the slight drag induced will not have a signifigant impact on the flight, perhaps only altering the trajectory by 0.1% or less.