0.2 is enough, doesn't really matter
I've used more than 30%, but maybe 20% would be ok
Any printer should be able to print this. I recommend to use ABS or Nylon, not PLA because of it's melting temperature.
First I've started to improve official Diamond team's holder - it's pretty good, but i've not fully satisfied with it's strict geometry and thick walls, so that part is designed from scratch. That give me a bonus - possibility to change license to one with Non Commercial part.