How it is with graphics? Can I use sprites which are free or must I paint the graphics during the jam?

I guess you can but it won't be judged in Visuals nomination:

1. Please only use assets you have permission to use, and avoid infringing upon any copyright or trademark.

2. Visuals: how visually-impressive was the game?     Note: only rate based on art assets created during the jam, not art assets created before the jam