If they were just continuing with the same continuity they could do that although Venom would still need his own movie. With a reboot I think it would have to be more like Superior Foes although maybe still call it Sinister Six just because it's a catchier name.

Sinister Six is normally about Spider-Man's biggest villains all coming together to mess with him, and they would need more set up. Superior Foes is more of a collection of C-list villains who are still generally more concerned with commuting general crimes rather then taking on Spider-Man. That's something that's more doable with this first movie.

With this Spider-Man having already been active for a year or two he might have already fought these villains, but if there motivations aren't entirely aimed at him that isn't necessary. Also with the MCU being older now I think viewers will be more on board with a multitude of villains just existing without having to go into all their backgrounds.

As for the line up I'm thinking mostly character who probably couldn't carry a movie as a solo villain. People have already seen Rhino so he'd be good to throw in. Shocker would be an easy one to throw in I think, and I know you were repping him as a solo villain, but I think Vulture works well for this too. Black Cat would good to throw in to add a woman to the team, and I'm thinking she might end up switching sides to help Spider-man by the end of the film, and maybe still get her spin off solo film after.

That leaves too more slots open. Not sure about the fifth member, but I was thinking the sixth could be Doctor Octavius who's kinda the mastermind of the group, and he might only become Doctor Octopus in the final act of the movie.