How to go about starting to build a 2D RTS

Hi everyone, im working on my second game and im just wondering where to start. I would like to go for the same kind of style as Prison Architect and Rimworld but instead go down a different route in terms of gameplay. I would like to make it much more like Command and Conquer. I have already started designing my sprite sheets and im ready to get some things into the engine.

This is the style im going for but with my own twist.

These are some early sprites that I have ready to get in game and start messing with. Basically I want to start doing two things.

  1. Get the background sorted correctly ( The world ) so the sprites can float around in the world.

  2. Get these two chaps to start killing each other.

I just dont know where to start particularly but I would like to try and achieve these two things.

Would really appreciate some advice.

All the best.

Rich