Just download what you like or need (3 or 4 holes, or 4 holes with teeth) and print it.
Thing can be customized via 123d Design app. Model in *.123dx format attached.
Here is 150mm length version without teeth and 140mm length version with teeth.
Hole for toothbrush is 10mm width, path to hole is 8mm width, it suits for all sizes of toothbrushes my family has.
To attach it to wall I have used double-sided tape.
Tooth model is used: http://www.thingiverse.com/thing:20214

upd. version 2 uploaded. stl+photo. 123d file updated.

Doesn't Matter

No

0.2mm

15-25% will be enough

Better to print it with 15-20 brim.
25% infill will give better results for top layers.

If you would get glossy thing, put it in dichlorоmethane bath for 30-50min.
Check dark-blue one on photo, it is after dichloromethane bath for 1 hour.