Hi lukas, and welcome to SRC.
Since you are new to the marine hobby, I would advice that you should start off with as big a tank as your budget or space allows. Small tanks are more difficult to maintain as they are less tolerable to any water perimeter swings, so do consider going for at least a 2ft tank.
If it is not possible to go for a bigger tank, then go really slow in stocking with a small one.
Cheers, and happy reefing!