Rashfords on and off form and mood and work rate, given his wages... He's just not worth it ultimately IMO. He's not good enough at what he does well to counter how little he does defensively on the pitch, and the mood swings. To add to that... Is he somebody who balances a front 3 of Hojlund and Garnacho to a high level? Not sure about that. Garnacho for me is better on the right anyway, but we can upgrade on Rashford, just as long as we can actually get a fair value for him (60m or so). That contract will be hard to deal with but I can see PSG being open to him replacing Mbappe.
So from a squad building perspective, we have to see from our group, who is the right profile and who is at the right wage to be either a starter or a depth player. I'd look to get rid of all our attackers apart from Garnacho, Hojlund and Amad. In midfield, I'd get rid of all the guys apart from Mainoo, Bruno and Casemiro. Maybe Eriksen as a backup deep playmaker for now, but probably replace. I don't think the others are the right profile for what their likely role is. From defence, I'd keep Shaw, Malacia, Martinez, Kambwala, Lindelof, Dalot and then possibly Wan Bissaka (depending on sale potential, but maybe I'd assume we can sell for more than we replace him with). I'd keep goalkeeper as is for now.
So that gives a squad of:
GK - Onana, Altay, Heaton
RB - Dalot, ???
RCB - ???, Lindelof, Kambwala
LCB - Martinez, ???
LB - Shaw, Malacia
DM - Casemiro, ???
DM (playmaker) - Mainoo, Eriksen
RW - Garnacho, Amad
CAM - Bruno, ???
LW - ???, ???
CF - Hojlund, ???
So to fill those spots with signings... I'd go:
RB - Dedić. High potential, very good on the ball, fast, wouldn't be too expensive
RCB - Todibo. Starting caliber, good age, quality on the ball and good fitness.
LCB - Pavlovic - haven't watched him, but based on FM and being left footed...
DM - Andre (defensive ball winner who is good on the ball)
DM (DLP) - Garner, should never have sold him.
CAM - nobody, Bruno doesn't need resting and others can fill in. Give chances to young guys like Shoretire or Hansen-Aaroen or rotate Eriksen in there.
Winger #1 - Nico Williams - can play either wing and rotate with Garnacho, a great direct runner with the ball, elite potential.
Winger #2 - Someone like Pedro Neto. Left footed, direct winger. Olise depends on cost. But this one is probably a long term rotation guy.
CF - Taremi - no brainer, would be on a free. Probably going to Inter though.
That gives a starting 11 and 2nd 11 of:
Onana
Dalot Todibo Martinez Shaw
Casemiro Mainoo
Garnacho Bruno Williams
Hojlund
Altay
Dedić Lindelof Pavlović Malacia
Andre Garner
Amad Eriksen Neto/Olise
Taremi
It's a lot of work, but it's definitely doable and not overly expensive options. It resets the age of the squad, it cleans up the wages, it gives good depth in every position where you have competition now and going forward and cover for every player, while also a fair split up to make sure every player gets the games they'd expect. Also builds in a transition plan for someone like Casemiro.