While it's impossible to buy 10 quality players in one window unless the team is called Barcelona (still don't understand that one) it is possible to get 10 players of mixed quality. Some decent, others top quality. Main thing is getting rid of the rotten culture so even if some are just decent as long as they are motivated and good team players the mix will be very good.
With regards to the budget I'd probably recruit something like
3 sure starters
3 rotationals
2 great dressing room players
2 promoted youths
Not to be underestimated
Barcelona used to have a guy called Pinto as their second goalie. The guy arrived from Celta Vigo I believe and that was probably his level. But the dude was hugely popular within the team and he was an older wise head. That guy didn't get stressed out by the pressure, on the contrary, he relieved pressure of others and helped create a good atmosphere. FIND "A Pinto"! Choupo Moting is that guy at Bayern today. I'm sure United have had their own Pinto before. Find a new one on the cheap, quickly.
Also, I really do get the Arnautovic move. AC Milan brought in Zlatan 2-3 years ago until his body broke down bit by bit. Mario Mandzukic was handed a contract a year or so ago but unfortunately he was totally shot. Then they brought in Giroud and he won them the title with a little help of the motivator Ibrahimovic.
Arnautovic has a good resume, was very good during last years euros, is talented and has passion. He could have been a decent back up striker as well as a fierce competitor teaching some of the sulks what it's all about. And if he had matured earlier he would have been close to world class, unfortunately he lacked proper guidance in his youth.