Many thanks for all the diverse and wonderful replies - such a great community here!
I have now made up my mind and will focus more on finding people I want to play "my" systems with rather than starting a more popular system just to find more players.
As concerning GW I will say this: If they ever re-do Mortheim, I will give it a try and I might have a look at their "The Old World" Project. So far however it will be Frostgrave and Warlords of Erehwon for me, which I consider the successors of the classics (in spirit, not necessarily rules-wise).
Every advice was much appreciated, thank you! Happy hobby-ing to you all and stay safe!