At what point does it all become too much? That's a lot of characters and it all worked fine in the context of SF, but let's not lose focus on these being James Bond movies and not Agents of SHIELD.
If anything, I'd like to see Leiter involved in the final attack on the villains like in NSNA or LALD.
Yes to Leiter! He should return!
A big yes to that. Jeffrey Wright is fantastic in the role. Enough time has passed for him to have moved on from South America.