Still kind of new. Is it possible to add mods to the game and host server so others can play and use the same mods?

I am hoping to add maybe something like a back pack mod or something that changes the inventory slightly. what would the best mods for this be? and is it allowable to do so while hosting multi-player? I have used mods before(just to play around with), but never in multi-player, nor do I even have the mods I used to have