You do not need a hundred of them. Just 8 (4 from the club), if you want to have a 25 men squad. Of course, it is not necessary to have a 25 men squad, many teams are completely fine with fewer players.
Currently, we have as homegrown:
Heaton
Henderson
Evans
Maguire
Shaw
Williams
McTominay
Mount
Voldemort
Sancho
Rashford
Diallo
with the italic ones being also club homegrown players. Assuming that we want a 25 men squad (again, this is not necessary and many clubs opt for less) we can immediately sell 4 of them and still be completely fine. Of course, hopefully soon more of them will leave, but by that time Garnacho would need to be registered, and he is homegrown too. Assuming that someone else from the academy might make it too (Mainoo, Hannibal etc) that would be enough to register 25 players in a couple of years.
And worse thing worst, if you have only 7 homrgrowns, you still can register 3 goalkeepers, 8 defenders, 6 midfielders, and 7 forwards. Plus an unlimited number of kids that are below 21 years old. Which should be more than enough.