Reworking home network to reach LAN from WAN

So I have thought the last few days about finally reworking my Network here at home to get the Firewall between router and Server. The problem is that my Network is not in a state where I can just move everything behind the firewall, so I want to get to a in-between goal of having security for my server, and if something happens, at least security for the rest of my Network. I work in IT, but still an apprentice, and haven't configured a Firewall myself yet. So take this image as my Current Infrastructure: The Double line is not yet established, but planned, (so the current connection can be s

Question by Shakran on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.