I really don't think BP needs characters or a villain that ties to the rest of the MCU to feel important. Instead, make BP, Wakanda and his mythos important. The MCU is already doing that a little bit, and the seeds have been laid.
Start pushing Wakanda as the new world superpower in the MCU which naturally makes people uneasy. Make his villains bigger than they usually are in the comics and give them a wider reach. Someone mentioned it yesterday that Killmonger's mission when we was king was acknowledged by Wakadan War Dogs in New York, London and Hong Kong. Address that one way or the other (hoping Coogler doesn't forget about that one way or the other) Wakandan spies should be something that makes SHIELD nervous (if they find out about them). Have T'Challa as a main player of the new Avengers, and have Nakia show up in a Black Widow movie (or better yet, put Natasha in a Nakia movie). There's so much you can do to make T'Challa and Wakanda feel very important to the MCU without borrowing villains and characters and having his movies being just another episode leading up to the season finale.
I think T'Challa taking on some kind of cabal or organisation would be fun, though it may lead to underdeveloped villains. Say figures of the neighbouring countries of Wakanda have conspired against the Black Panther. Princess Zanda, Achebe, Moses Magnum, M'Butu all working together, inflitrating Wakanda's refugee programs, outreach centres and so on with the backing of Western countries.