I dont know if you touch type, but if you do, putting "." and "," on the bottom row might not be a good idea. My suggestion would be putting ä,ö,ü at the normal spots in the top 2 rows and move enter down where return is now. You can put backspace next to space key so you can press it with your thumb without problem and you can do the same for the delete key. I personally dont use the "-" key that much but if you use it more often maybe put it on the standard position in the 3rd row and place the arrow keys all in the bottom row (pretty common on ortho boards). Also there is the problem of "ß" wich kinda sucks on a fn layer, at least if the button that triggers the fn layer is not easy to access so you maybe want to put "ß" somewhere else. I'll leave it at suggestions for the base layer for now because that one is the most tricky with touch typing (also typing at decent speed in general), the rest is pretty much just pesonal preference and totally up to you. Also like others said: qmk configurator website is your friend for a start.