In essence, this movie will unify the two previous Spiderman movies series into a single multiverse so they all become 'cannon."
That could get complicated. So...3 different versions of Aunt May, 2 of Uncle Ben, 1 Mary Jane who is not to be confused w/ the current MJ, 2 Gwen Stacy's, 2 or 3 Green Goblins (was James Franco Hobgoblin?), 2 Dr. Curt Connors (but he was only The Lizard in one of them), 3 Flash Thompsons. And 2 versions of Eddie Brock if you count the Venom movie, would be kinda hard not to incorporate that in the MCU if they are tying all the Spider Man series together. Huh, I didn't even realize that Betty Brant is a recurring character in Spider Man canon. Elizabeth Banks plays her in the Tobey Maguirre movies, Angourie Rice in the current iteration.
And that doesn't even take into account "Into the Spiderverse" which you mentioned, which would bring yet more versions of several of those characters, plus Miles Morales. Can we get a live action Spider Gwen? Then we could have Hailee Steinfeld in the MCU.
Looked up the cast list (I'm sure it's not complete, they probably want to keep some surprises). Jamie Foxx is back as Electro, from the 2nd series.
Really doubt they'd bring her back, a minor character, but would love to see Mageina Tovah return (Peter's neighbor/landlords daughter in the 2nd and 3rd Maguire movies).
I kinda can't believe some of the actors who have appeared at some point in the various films, in small roles. Felicity Jones, Sarah Gadon, Aidy Bryant, Skylar Gisondo, Peyton List in a role so small it was uncredited.