Do I need to register as self-employed or Freiberufler in Germany if I want to sell on Gumroad and such?

I americium a designer/illustrator/artist and I americium soon moving to Germany (from different EU personnel state). I was hoping to waste my artworks and integer equipment connected Gumroad/Lemon Squeezy/Figma organization etc. arsenic a hobbyist. But first I wanted to trial and spot what sells and for that I was hoping to put immoderate mini integer equipment connected Gumroad for €0,00+ (pay what you want). Once I understand nan market, I whitethorn waste for predefined value (although I americium not judge really overmuch sells I tin make fixed I person almost nary societal followers aliases trading skills). My mobility is:

Do I person to registry arsenic a self-employed personification earlier testing nan water?

If my merchandise costs €0,00 and group still pays (On Gumroad aliases BuyMeACoffee), will it not beryllium considered donation? Are those subjected to taxes arsenic well?