Not sure how much experience you have as a game developer but RTS games are extremely challenging, difficult to design, balance and test.
Unless you've developed other games before I would set your sights about 80% lower. Make a pre-RTS like game, either Tower Defense or a sort of MOBA. Scale it way back to a handful of units, then experiment with multiplayer.
C3 does have its limitations (like any engine) and NWjs has performance issues in general, nevermind taxing it with 1000s of objects. *remember each unit could easily have multiple objects attached to it: a muzzle flash, some sort of particle emitter for showing movement, fx, bullets, animations, minimap object, nevermind background art etc...