i think its better to start with a join movies&tv comm, you probably want to grow it fast and managing two new comms may get to confusing/tiring for the mods, plus it will be the mods the main posters there until it gets big enough
since its a general comm, it a good idea to have it on an instance that its federated to most big intances so lemme and lemmy.ml are good choices, with lemee being a bit better because of lax moderation and i think making comms there is easier