I want to make a "game" which is more of a game environment sandbox. something kind of in-between game engines and actual games. I want to be able to create the feel of different game types like FPS, RTS, top-down adventure, side scroller, whatever - within a certain set of consistencies of my choosing. Like something to toy with different ideas for game mechanics in different settings while not needing to explicitly manage things like what a wall or door is each time i change things (things that would be defined as part of me creating the "game"). I want to be able to invite a friend into test environments as well (so multiplayer needed). I am expecting to need to make edits to the game mechanics outside of the game, possibly even through adding extensions to whatever game engine i use - so i will not be looking to set up a UI for tweaking settings. Just something that makes it easy to make changes to how the game functions, easy to spin up a dedicated server to run an instance of the created game environment, easy for another person to join that environment.
Advice needed is: is this scope feasible for 1 person and what game engine should I look into for trying it out? I am not trying to do anything particularly fancy; no overall game design, no story, minimal amount of textures and assets. Literally just an environment to toy with game mechanics.
I understand there is so much below the surface of what I am trying to do that I dont understand, i.e. I have seen an example for all the decisions that need to be made about doors, how interactions work, size, how changes are managed (this door, or all doors?) etc.
Basically, I am not trying to send my friend a new .exe everytime I make a change to a game mechanic - since that's expected to happen a lot as the primary use-case for the thing. If I add assets, then yeah - although ive seen games have the ability to download assets when connecting to the server, so maybe not even that. Ideally, I'll have a fixed set of assets that cover everything of interest, and the way they are rendered and the multiplayer networking and all will be consistent throughout.
hopefully this all makes sense