That' a fair point raised by legendkillin up there; some of these Avengers aren't completely practical; T'Challa is the King of a Country, both Doctor Strange is the Sorcerer Supreme. It's not like these characters [should be?] invested in stepping out every time the Earth comes under threat; at least (in the case of the latter) it's under a mystical threat of some kind.
Thus, based on that, the team needs to be more ... mobile; a group of people that don't have any other (specific) obligation other than being an Avenger, so I think it'll come down to a select few; maybe six or seven, of which will include both Scott & Hope, in addition to Wanda (if she survives Avengers 4 and doesn't go training with Strange), a mix of (depending on survival) Sam, Rhodes & Bucky, and Carol in the lead.
Characters like Black Panther and Doctor Strange may feature, but I'm not fully expecting them to become [active] Avengers - just because they were in the comics, they don't need to be in the MCU, especially when we've got so many more characters to yet introduce.
I would also agree with the concept that we're not likely going to see another Avengers film anytime soon; instead I think we'll get (kind of) ensemble films; maybe Bucky in Black Panther 2, or Wanda in Doctor Strange 2, or Hawkeye/Falcon in Ant Man 3, that sort of thing.