Symbiote and Sinister Six. Following Gwen's death seems like the perfect time for the Symbiote and it'd feel odd to have all that setup in TASM2 not lead to a Sinister Six team up in the sequel. However I think it'd take a lot of care to not make it feel over-stuffed. So Sinister Six as the villains with Goblin (I prefer Doc Ock as the leader of course but it doesn't make sense with the setup we have here), Rhino, Mysterio, Sandman, Vulture and Shocker. Have Shocker be Uncle Ben's killer to finish that dropped subplot, but don't have it be a coincidence. Have Harry deliberately find him and give him the weapons as a way to shake Peter. The Symbiote can be introduced via Oscorp (not that they'd make it, but have them be in possession of it and experimenting on it). Have Peter come in contact with it at some point. It grows to consume him over the course of the film and he has to separate himself from it before the final battle with the Six. Mary Jane can be teased throughout the film but only appear at the end.
The next few I'm rather unsure about rights and such but just dreaming here.
Make a Miles Morales movie set on another Earth.
TASM4 with Eddie Brock Venom. Mary Jane and Peter's relationship just starting to build. Bring back Flash Thompson, having returned from war without his legs. Have Peter working at the Bugle.
Do a Miles sequel, a Spider-Gwen movie and a Flash Thompson Venom movie.
TASM5 perhaps can be a Doc Ock story of some kind.
A third Miles movie and Spider-Gwen sequel, along with a third alternate universe Spider-man movie.
TASM6 can be a bit more ahead in the future and a loose adaptation of Kraven's Last Hunt. Peter can propose to MJ in the end of it.
A third Spider-Gwen and another alternate universe Spider-man movie.
And finally the universe can end with a story based on the general idea of Edge of Spider-Verse, crossing over the main TASM series, Miles, Spider-Gwen and the two other alternate universe Spider-man films as well as other universes.
At least that's what I can come up with at almost 2 in the morning.