Put it together in tinkercad, pretty basic but works (I think)

Revised version has holes for brushes 6mm 8mm 10mm

Also the first versions paints pots don't seem to print too well, end up with the lots of lines in the hole, so have changed it to just holes now instead, removed some of the trim around the edge off the top, made it slightly a different shape overall

Third revision

Reduced overall height to 5mm, added 4x 4mm holes for smaller brushes, added a further 6mm and 8mm for a total of 9 brush holes.

No

Any

Prints fine in 0.3mm for speed, still takes 2-3 hours depending on walls and bottom/top layers