Technically, Stardew Valley multiplayer was designed for four players, but technicalities have never stopped modders before and they're sure as hell not going to slow their roll for Stardew Valley, of all games. Case in point: Community Farm, a content pack by modder SgtPickles which comes fully loaded with a massive 156x156 map and support for 10-person multiplayer.
Not long after Stardew Valley multiplayer came out, modders worked out how to remove the player cap so all your friends (and all their friends) can play on one farm, but that still left the issue of building everyone a cabin without turning your farm into a cramped neighborhood. I'm not sure if Community Farm is compatible with the Unlimited Players mod, but I dearly hope it is, because it could solve that problem by giving everyone some wiggle room. In any case, it's a great map for large friend groups who want to farm together. Have a look at the whole, massive thing:
You and all your friends will need the Stardew Valley modding API (SMAPI) and the map pack MTN (More Than Necessary) to get Community Farm working. Visit its Nexus Mods page for download and installation instructions.