A number of years ago I completed an MMO project by myself (art, programming, marketing, etc). It was fun! Real-time server was in Python Twisted, lots of Cython to speed up the deepest parts of the game loop. Django for the main website. The client was Flash (this was back in 2013, when it was still kinda a thing), which meant anyone could jump in really quickly, but technically that was challenging for a real-time 2D Zelda-style game because you were limited to TCP rather than UDP and the server has to be 100% authoritative since opening up Flash swf's or sniffing packets is so very easy. The server could support 250 people, and I had some fun tooling that let me spin up virtual players to stress-test it. Fun to remember!
The thing with MMO projects that really gets you is, even after you've got a mature client and server you still need to put together enough content, which if you're level designing/writing/painting everything yourself, is an enormous quantity of work. If you don't want players to run out of quests and whatnot you've probably got to lean towards a sandbox experience, and this MMORTS is a particularly interesting way to go.