You can try Lyra project. It has many subsystems done and ready. Like lobby, multiplayer, hardware settings etc. Granted it is aimed at FPS games, but you can adopt it to RTS (imo less work than creating all those subsystems).
Lyra is not easy to understand, but it is mostly data driven, not code. You getting at quite complicated project (for first game) anyway.
Anyway Lyra or not, start very small. Limit scope of that RTS, make just few systems, like gui, selecting and moving units, not much more. And there is biggest trap: “comfort zone” do not drown yourself in stuff you know how to do. ie. level design. Go for things you do not know.