First off after seeing Captain America Civil War, Falcon, Scarlet Witch Ant Man and Hawkeye were recently imprisoned in the Raft by Secretary Ross but in the end they were freed by Steve Rogers and they are now on the run from the law hiding and since Spider-Man Homecoming is set to feature multiple Avengers, Captain America, Scarlet Witch, Falcon, Hawkeye and Ant Man are now expected to show up to help Iron Man and Spider-Man deal with the Vulture and some of the other villains that are yet to be confirmed.
Now the reason why Captain America, Scarlet Witch, Falcon, Ant Man and Hawkeye would be the only other 5 additional heroes to join Iron Man and Spider-Man in Homecoming for next year is for these following good reasons
1. Bucky is right now put into suspended animation so that King T'Challa the Black Panther and his people in Wakanda can find away to remove the brainwashing from his mind while he is kept safe from the government
2. Scarlett Johansson is busy with other movie projects right now and her character went dark after helping Captain America and Bucky escape to Siberia but also despite her betrayal to Team Iron Man, she wouldn't watch anyone's back so clearly she is somewhere on Earth on her own so she won't be back until Thor Ragnorak
3. Vision is at the compound looking out for Rhodes who no longer can fight after accidentally getting shot by him and are still initiative members of the accords
4. Another good reason to why the 5 heroes on team Cap should appear in Spider-Man Homecoming to help Spider-Man and Iron Man deal with the villains in this movie is because Scott Lang/Ant Man is set to return for the Ant Man sequel titled "Ant Man and the Wasp" and having him start out in that movie currently while in exile with Team Cap wouldn't do any good and having the team wait until Avengers Infinity War Part 1 to be wanted back to save the world would be too last minute so Spider-Man Homecoming should be the film for Steve Rogers and his crew to start earning back the world's faith in them
Now for the villains that Marvel is due to confirming right about now
Vulture who is rumored to act as Spider-Man Homecoming's main antagonist is due to have his actor announced and since Michael Keaton backed out of playing the character for no reason other than scheduel conflict, Kevin Feige and Marvel Studios need to cast a different actor for the role like Mark Strong or Christoph Waltz because both those actors are well known for playing villains in movies, either one of them should do but also lets hope Marvel doesn't go casting anyone like Sharon Stone or the wrong kind of actor for the part because the last thing we all need is more casting controversy like Tilda Swan as the Ancient One, so either Mark Strong or Christoph Waltz will do for the Vulture
Now as for the other Spider-Man villains that Marvel is yet to announce, one of them is said to be non white meaning that Marvel might actually do another race change who would probably be the Rhino
now for anymore villains that Marvel Studios may include, each one of them has to match up with each of the heroes that are yet to join in and the villains Marvel should consider including are
Scorpion
Shocker
Kraven the Hunter
and Mysterio
Of course Adrien Toomes would have to provide some of these guys with their gear and costumes or if Spider-Man has fought them before he would have to break them out and get them to join him as members of his Sinister Six and with this Spider-Man reboot only having one director for the job, the other 4 to 5 villains along with Captain America and his Avengers won't be expected to turn up until we come close to the film's climatic battle. For now we wait for more casting on the movie to be made and soon because lots of fans are so thrilled to have Spider-Man on board in the Marvel Cinematic Universe and are not gonna want Kevin Feige and Marvel Studios wasting anymore time hesitating.