The case is printable very easy, if you print it with the backside down. Then support only generated inside the case, where nothing is visible on finished build.
The front of the case should printed with the speaker-mount upside.
Resolution and infill are only recommendations. Infill can be higher if you like to have a more stable case. I prefere to print with minimum 2 perimeter outlines (0.4mm nozzle).
To hold the edges on the heatbed I use 4mm brim.