Goalkeeper -> Onana will be the number 1, certainly. I would expect Altay as a backup as well.
Right Center-Back -> I think Lindelof will enjoy a second life with Amorim and that will surprise a lot of fans. Dalot can play here as well.
Middle Center-Back -> I think De Ligt and Yoro will be options for this position. People keep mentioning Yoro to play RCB, I believe he has no chance of playing there, he's too simple/practical on the ball, not creative enough in the buildup possession.
Left Center-Back -> Martinez is in theory a good option, but he's not exactly a classy playmaker like the coach appreciates. Maybe we'll see some signing here... like Inacio or something
Right-wing -> Diallo is probably gonna thrive here. Dalot and Mazraoui are not pure dribblers or great 1x1 offensive devils, so it might be hard for them to escape the back three. Unless...
Left-wing -> It might sound weird, but I'm 99% sure Garnacho will end up here. So there's a chance Ruben ends up playing with a more deffensive RW (Dalot or Mazraoui), someone who can join the back three when the team loses the ball and has to defend a counter-attack, making a 4-back line and allowing Garnacho to stay more upfront. He has used this strategy sometimes at Sporting, this would mean that while the team would attack in a expected way, it would defend with a back four line (back three + right wingback), 4 guys in an intermediary line (Garnacho left, the right forward on the right and 2 midlefields in the center) leaving left forward (Bruno) and the striker upfront. Shaw or Malacia as backup I would say.
Defensive midlefield -> Ugarte will thrive. I'm curious if Casemiro is staying another year as a backup or if Amorim will sign some younger DM.
Central midlefield -> Kobbie Maino will probably be a starter and will fit well. I would expect a signing here to add another player to KM.
Right forward -> Here, no one fits very well. Antony I'm pretty sure will be released. Maybe we see Mason Mount having a second life as a backup? At least one signing for sure, maybe even 2.
Left forward -> Bruno will play that 10 position, leaving the left flank for Garnacho and playing in a more inside central offensive midlefield position. Maybe Rashford will stay? I I think Sancho would have a word to say if he had stayed.
Striker -> I wouldn't expect great changes here. I think Hojlund will be the bet for main striker and Zirkzee as his backup.
So basically I would expect these signings for sure, between january and the summer market:
-> LCB
-> CM
-> Left-footed offensive middlefield/interior winger (big signing; someone with Foden or Palmer's carachteristics)
And these maybe (or not):
-> Deffensive middlefield
-> Another left-footed offensive middlefield/right interior forward
-> Right-footed offensive middlefield/right interior forward
I would bet on something like this:
GK - Onana (Altay)
RCB - Lindelof (Dalot/Mazraoui)
MCB -> De Ligt (Yoro)
LCB -> Martinez (Signing)
RW -> Dalot/Mazraoui (Diallo) -> very different options for different games and oponents
LW -> Garnacho (Shaw/Malacia) -> the same from above
DM -> Ugarte (Casemiro or signing)
CM -> Maino (Signing)
ROM -> Signing (Mount)
LOM -> Bruno F. (Rashford or signing)
ST -> Hojlund (Zirkzee)
For each of the wings, one more offensive option (Diallo right, Garnacho left), one more deffensive option that allows the guy from the opposite flank to not focus so much on deffending (Dalot & Shaw/Malacia)
Martínez can outpass almost any centre back in the world, Inácio included IMO. The issue with him will be in my opinion that he's not suited to be a wide defender. His limbs are too short, and he's not quick enough to eat up big spaces quickly. We saw how big of a problem this can become in the game vs Porto, although it isn't his fault that he was put into such an exposed situation when his skillset is totally different. However, his in-possession qualities like line breaking passes, etc. won't be a problem. If anything, they will be the reason Amorim will try to find a place for him in the XI IMO. However, I can't consider him for the CCB role (despite him having the best and most passing angles in the centre) when the squad already contains two of the best CCBs around in Maguire and De Ligt. Martínez is not in this bracket, he's far from it, overall.
Yoro will have to play LCB or RCB because he's by far the most qualified for the wide defender role from all of our defenders, whereas De Ligt and Maguire can only play CCB, and I think one of them will always start, but both of them never will unless an injury crisis happens.
Lindelöf or anyone else in the squad cannot cover big areas and eat up big spaces quickly like Yoro can. Funnily enough it's probably Evans after him that's the best at this. I'm certain that Amorim won't put two slow defenders around De Ligt / Maguire in the centre of the defense. Any PL team will destroy us on transitions that way. I expect Yoro to be our starting RCB with Evans and Lindelöf being his back-ups in that position.
Yoro is also the best suited CB we have to help out De Ligt / Maguire with his recovery pace if they make an aggressive interception but don't win the ball, etc.
I agree that an LCB is going to be signed in one of the next 2 transfer windows, and it will be another space-eater like Yoro, probably Branthwaite.
However, I'm not sure what you mean by a "Palmer or Foden type" right forward. They're two completely different players and I think they thrive in different circumstances as well.
Someone like Foden next to Bruno, but behind the striker, could be useful to us in theory, because their very good ball striking could often be taken advantage of, if our right hand side and players around him generally, was set up to make space for him, so they can receive, turn, and shoot in favorable zones with enough time on the ball. Also, someone like Bruno could definitely give this player great chances on a silver platter on a regular basis. Hojlund's hold-up play and channel running capabilities could also come in handy, as well as the overlapping wing-back which is a role that Dalot and Mazraoui could both fill to a decent level IMO.
Palmer, on the other hand, is someone you want to give the ball to, because his passing range is excellent and he can also carry the ball much better and over bigger distances than someone like Foden...although we sort of already have Rashford for these things I listed, and I personally think Bruno is a better and more creative final third passer than Palmer is, but Palmer has the better passing range generally, and better diagonals.
In all honesty, I'd love Mount to become a viable option for this role, because he's our best off-ball player IMO with his excellent work-rate and disciplined pressing game. He's also a good striker of the ball, so we could create plenty of situations for him as well, where he just needs to put the ball into the net from a good chance.
(But there are surely some interesting options on the market too)