We already know that John Doe and Sweet Tooth will have major roles in the TV series by Playstation Productions.

Not sure I agree with John Doe being a major character to be honest, but it is what it is, so that kind of leaves room for just about anybody to be in the TV Series. Seriously, not even a psychic would have guessed John Doe as the central character. Nobody ever said "Oh I love Twisted Metal... that game with Sweet Tooth and John Doe". He's not even the best of the Roadkill drivers. If Doe is in even a scrub character like Melvin the midget from Twisted Metal 4's cutscenes has a chance of being in the TV series.

I picked the most likely candidates but likely your choice isn't even on the poll so please share.

Why I picked these 7;

Mr. Grimm
Grimm has been every Twisted Metal, in some form, so I'd be very surprised if Grimm wasn't in the TV Series. Even Death Race had a Grimm!
Now what form will Grimm take, who knows, but does he deserve more or less screen time? Is Mr. Grimm better as a mysterious force or a well developed character? Should there be a lot of supernatural characters like Mr. Grimm, Minion, etc. in the TV series?

Calypso
Calypso runs the contest, grants the wishes, and the one single comic book with Twisted Metal in the title is a story about Calypso, so why shouldn't he have a big role? Because they might want to tease the audience long enough before actually revealing the character. I just get the feeling they wont show Calypso until maybe the end of the season to keep the story mysterious. Would you like more Calypso? Should Calypso's daughter Krista Sparks (Grasshopper) have a role?

Preacher
Preacher is Sweet Tooth's greater rival, not John Doe, so Preacher should be a main character. A live action Brimstone would look great. Hopefully Preacher makes the cut as a major character, it would make the show better just having a psychotic holy man involved.

Dollface
I doubt Mr. Ash is making a comeback (sadly) so if Darkside returns we will likely see Dollface return, but hopefully it's nothing like the 2012 version of Dollface. Probably wont be like the original, I'd expect a completely new version of Dollface like how they've approached John Doe.

Axel
Axel is too crazy of a character concept to pass up, and most memorably appeared in Twisted Metal 2 where he stole Sweet Tooth's spotlight and since then carried on in every game but his first appearance was his most memorable. Might be that the character concept is a bit too crazy for even the Deadpool writers and Axel will not be on the TV series, but Axel would certainly make an interesting on-screen character. I could see many memes coming out of it.

Agent Stone
Unlike the other law enforcing characters of Twisted Metal, Agent Stone actually had a cool name. The first Agent Stone was a secret spy 007 Bond type of character and the 2nd was an unlucky suicidal but skilled police officer. For an action comedy I'd expect a more Crimson Fury-ish Agent Stone to appear, rather than the depressing version.

No-Face
How dope would No-Face (Crazy 8) be in the TV series? Would love to see an episode of Twisted Metal from his perspective but I imagine getting the look of the character down for a live-action filming would take a lot of work. I chose No-Face because ironically he was the new face of Twisted Metal when Twisted Metal: Black came out. Sure, Sweet Tooth's face was on the cover, but look at the game's manual, it's No-Face's Journal. He was meant to be an important character originally, so maybe the TV series will continue that character's legacy.

Other
There are many other characters that could get adapted. Bruce Cochrane, Hammerhead Mike, Mortimer, Raven, Mr. Slam/Simon, Jamie and Buzz, the Watts twins, Billy Ray, Angela/Amanda X, Black, Agent Orbital, Club Kid, Captain Rogers... The thing is just about every character I mentioned is unlikely to have huge roles. There are exceptions of course, like Krista Sparks, Charlie Kane, characters like that by whom they are associated with are elevated to major characters, but while Hammerhead, Thumper, and Outlaw are seen as important to lore to the fans, Hollywood writers may just see those characters as cannon fodder. I just get the feeling we will see a lot of expendable characters on the show, and maybe we will see a lot of familiar vehicles driven by original characters so while we might see Twister blow up we may not necessarily see Amanda Watts blow up, and it can give the writers a lot of freedom in killing off familiar vehicles without killing off familiar characters. We already know TV John Doe will be nothing like TMB John Doe outside of the memory loss, for example, so we might also get a lot of familiar character names attached to unfamiliar characters to further complicate the matter. But the bottom line is I guess you can't really expect any faithful character adaptations so if you're worried they might butcher your favorite Twisted Metal character you probably don't want to see your favorite characters involved.

Factions makes sense for some characters, particularly the masked ones, since it's easy to write those characters as a cult or other type of faction leader.
It would be very Mad Max-ish then but in a video game/comic book style. We definitely need more story details though.
The lack of info on Calypso is disturbing, isn't it?
The story so far is an outsider named John Doe, a milkman with memory/ego loss, and his car thief friend are hired, presumably for money but maybe on the promise of a wish, maybe by Calypso as a ruse/or someone else for a different reason, to deliver a mysterious package across a post-apocalyptic wasteland, which suggests maybe that wasteland has hosted previous Twisted Metal contests and is a bit of a no man's land.
What is the significance of the package and are they aware of its contents?
The obstacles they face are likely other drivers challenging them for the package,
but who sent those mercenaries?
Is Calypso just playing a big old game on everyone?
Probably.
It could be a last man standing style contest where whoever is last standing with the package gets the prize of the package, which is one wish.
Or maybe I'm way off.

But who is the car thief friend of John Doe anyway?
We guess they are driving Roadkill, a junk car or a junk muscle car, but the detail of his friend being a car thief could suggest John Doe drives several stolen cars in the series. That would be kind of interesting. One episode Doe & friend is driving Mr. Slam and next episode Doe is in Shadow. That would be a very TMX-ish concept for the TV series.

And I'm glad you bring up the Roberts LAPD officers as major characters because I'd like this debated.
See, as Twisted Metal fans we all know Jamie and Carl/Buzz Roberts are important. They are the law brave enough to take on Calypso.
Carl Roberts is one of the few original TM1 drivers that appeared in multiple sequels. Jamie is one of the few badass females TM has.
Their series story is a big what if scenario though, and they were left in limbo.
First, Carl (or Buzz) had to survive his wish backfiring in TM1, which was miraculous enough, and is only saved if Jamie wins the following year as Outlaw 2, otherwise he dead.
Then they only finally become a duo in Twisted Metal 3 (retconned) and Twisted Metal Head-On where they are given bad endings that do not continue their story.
In 3 their attempt to fix the world leaves them broke without jobs, and in TMHO the sibling rivalry becomes a big problem and Calypso wins.
The original Outlaw was put in Limbo. They favored Agent Stone's Outlaw 2.0 for the 2012 game, going for the Twisted Metal Black look, so Carl and Jamie Roberts were forgotten.
I think they can still end up in the TV series, but I just imagine them being used little, because I doubt they'd want that sober police officer perspective.
And if the show is set in a wasteland it's hard to imagine police all the way out there, but a police officer did end up in Silent Hill so I guess it could happen.

Minion would be cool, but I imagine that would be mostly a CGI character haha.
If they are going to use a Boss character they have to use Minion though, for sure.
Season 1 is too early for anything else, nobody needs to see Dark Tooth yet.
Maybe WarHawk would be cool to see though. Unlike the video games where flying doesn't make sense for Twisted Metal, for a TV series I'm totally fine with seeing some aerial action.