Certainly, we have the precedent for them using BST Hyde Park for a comeback show in the UK given this is what they did in 2017 when they came back after being away for a while. I would know given I went to that one.
It feels like the favourite is Thomas Tuchel, although having another Eredivisie title winner as their assistant manager in Ruud van Nistelrooy (formerly of MUFC as a player, ofc) feels like another option.
Moyes is absolutely not ending up back at Old Trafford and I'd double check where you may have heard that.
£21 would be just under £44 for inflation rate. I think it's left the inflation rate for dust at this point.
Also as an MK local I wasn't aware Springsteen had once played the Bowl until reading it in Ted Kessler's book.