Multiplayer Hero Shooter MVP Backend

I already have the roster, abilities, and map concepts locked in; what I don’t have is the backbone that will let players actually jump in and shoot each other. I need an initial PC-only build that proves the concept and scales cleanly as we grow... (Budget: $750 - $1500 USD, Jobs: Backend Development, C# Programming, Django, Game Design, Game Development, Game Testing, Node.js, Python, Unity, Unreal Engine)