Here is a list of heroes, villains and other characters that Marvel Studios are to focus on including for Iron Man 4 and more films within the 4th Phase of the MCU along with the actors and actresses to play them
Avengers
Robert Downey Jr as Iron Man
Before Robert Downey Jr. thinks about retiring, the famous Iron Man actor himself needs to stick around for a little longer after Avengers Infinity War Part 2 because he as Tony Stark needs to deal with the militia that abducted him in Afghanistan along with their leader, the Mandarin (who is sure to be the actual Mandarin that Tony is yet to confront but hasn't due to complications and distractions that occured in Iron Man 3) as well as having to discover more of his past and his return in Iron Man 4 along with the film itself needs to happen after Avengers Infinity War Part 2
Chris Evans or Sebastian Stan as Captain America
While Steve Rogers' fate in Marvel Phase 3 is yet to be decided, whether Chris Evans will still be around as Captain America after Infinity War or not which leads to Bucky taking over the mantle remains unconfirmed for the time being
Mark Ruffalo as Hulk
As Marvel's strongest hero, Hulk is sure to make it through Avengers Infinity War alive and hopefully during the planning for the set up of Phase 4, Marvel Studios will reaquire the rights from Universal so they can do more Hulk films so they can bring out more characters from the comics into the films who are on earth
Chris Hemsworth as Thor
As the mighty god of thunder, Hemsworth's characters is sure to have more enemies to fight in the MCU and his character is sure to have more adventures to explore with the other heroes too
Tom Holland as Spider-Man
As the actor playing everyone's favorite Marvel Comic Superhero, Feige and Marvel Studios should definately have the actor's contract extended for 3 to 6 more movies in the MCU after Infinity War so that more heroes, villains and friends can be present in the franchise along with Marvel's chance of including film's based on the most science fictional storylines like the Spiderverse but with the first additional 3 revolving around Spider-Man (Tom Holland)'s world
Evangeline Lilly as Wasp
As one Marvel's current fan favorites of the current decade, Wasp (as Hope Van Dyne) is sure to return for more action as Lilly's multi picture deal is sure to last for a dozen more films after Infinity War and is sure to have a big part in the 4th Avengers movie
Elizabeth Olsen as Scarlet Witch
While many fans are hoping for Olsen's character to make it through the Civil War movie alive, Scarlet Witch will be sure to appear in some of the phase 4 movies with two regarding her yet to be confirm spin off and the 4th Avengers movie
Scarlet Johansson as Black Widow
As the studio's fan favorite hero that they don't want to kill off, Johansson is sure to make it back for another phase as her character's stand alone is still on board for development
Chadwick Bosman as Black Panther
The King of Wakanda and silent member of the Avengers, Bosman is set with 5 films total on his multi picture contract which shows that he will be back for the sequel based on his character and the 4th avengers movie
Paul Rudd as Ant Man
As the second Ant Man, Lang is sure to return along with Wasp (Hope van Dyne) for the yet to be announced Antman Threequel and to assist the Avengers on taking down the Masters of Evil in the 4th Avengers installment
Jeremy Renner as Clint Barton/Hawkeye
The archer of the MCU, Renner is sure to be back for more action and his character is sure to start training his protege Kate Bishop and by the end of the fourth Avengers film, Barton is sure to be killed in battle with the Masters of Evil since Renner is getting old and Kate will eventually take over the mantle
Benedict Cumberbatch as Doctor Strange
With the chances for more sequels on the line, Cumberbatch is sure to reprise his role as the sorcerer supreme while exploring more of the MCU's worlds with him
Daisy Ridley as Kate Bishop/Hawkeye
Having inspired many with her role as Rey from Star Wars the Force Awakens, Daisy should be the prime candidate for Kate Bishop since she proved herself to be strong and independent in the film thus becoming the perfect actress to succeed Jeremy Renner as Hawkeye after Phase 4
Kelly Rorhbach, Teresa Palmer, Rhonda Rosey or Emily Blunt for Carol Danvers/Captain Marvel
While the actress for the kree powered superheroine is yet to be announced, Marvel is sure to do a sequel for the 2018 film and choose a specific actress for the part
Paula Patton or Megan Fox for She Hulk
as the hot and dazzling cousin of Bruce Banner, Jennifer Walters will be due to appear in the 4th Phase of the MCU with Banner saving her life by blood transfer, which will turn her into the She Hulk and help him protect the world from its most destructive threats
Masters of Evil
Lee Byung Hun as Zhang Tong/Mandarin
As the real Mandarin of the Ten Rings Militia and cult, Lee Byung Hun would do an excellent job on portraying the character's proper and actual MCU version but he won't be a chinese dictator, instead Lee's character will blend in with the more civilized world of the franchise so that his depiction won't be too provocative like Ben Kingsley's portrayal in Iron Man 3 if the twist wasn't done and Kevin Feige along with the rest of Marvel Studios will definately make sure that Lee's Mandarin will wear the ten magic power rings each on all ten fingers and when battles RDJ's Iron Man, he will also wear the same kind of armor the character wore in Iron Man Armored Adventures and Marvel Disk Wars The Avengers which should make the Mandarin's portrayal in the MCU more appropriate than in the comics and more inspiring worldwide. Whether Lee's character will be the same original warrior king Jackson Norris mentioned or the second person to don the mantle and the rings is yet to be revealed and while the legendary backgrounds on the villain may have ties with South American legends, Zhang as the Mandarin will serve as the main antagonist in both Iron Man 4 and Avengers 4 where he will act as one of the two leaders of the MCU's Masters of Evil since he is very powerful with all ten power rings in hand and highly trained in the martial arts.
Daniel Bruhl as Baron Zemo
While confirmation on Bruhl's return as Zemo is yet to be made, he will partner up with the Mandarin on leading the Masters of Evil into battle against the Avengers and taking over the world.
Keir O'Donnell as Mac Gargan/Scorpion
An enemy based on the predator of a spider who was aggravated by the side effects of his transformation, Scorpion would make an excellent member of the MCU's masters of evil to rival Spiderman
Kevin Durand as Herman Schultz/Shocker
An enemy of Spider-Man with two air blasting gauntlets that can blast through almost anything
Sean Penn for Valentin Shatalov/Crimson Dynamo
Leader of a Russian separatist terrorist organization who will act as the primary antagonist for Iron Man 5 and will later join Mandarin Zemo and their Masters of Evil in Avengers 4.
Rosie Huntington Whitley or Karolina Kurkova for Amora the Enchantress
An enemy of Thor and a notable member of the Masters of Evil skilled in sorcery. She will be expected to debut in the yet to be announced fourth Thor movie in Phase 4 before joining the MCU's line up of villains forming the Masters of Evil.
Gerald Butler or Jason Mamoa for Skurge the Executioner
An enemy of Thor and ally of the Enchantress.
Nonso Anozie for Man Ape
Leader of the white gorilla tribe that rivals the Black Panther tribe who will appear as the main villain in Black Panther 2 before joining the Masters of Evil for their support of regaining control of most of the African territories.
Adam Driver for Morlun
If necessary, Morlun would appear in the yet to be green lit Scarlet Witch film in Phase 4 as the film's primary antagonist where he would be destroyed in the movie and later resurrected by the Mandarin to join his Masters of Evil in Avengers 4 and later as the main villain for a future Spiderverse film.
Stephan Amell for Wonder Man
a metahuman who acts as a member of the Masters of Evil before changing sides with the Avengers
Erin Richards for Moonstone
A rival of Ms. Marvel who would join the MCU's Masters of Evil to oppose Carol Danver
Irina Shyak as Dragonfly
A villain that will join the Masters of Evil to rival Wasp.
Feel free to comment on this list of heroes and villains for Phase 4 and make sure that Marvel does films like Iron Man 4, MCU Spider-Man 2 and more right before they announce the films for the next Phase as well