I think we need a minimum of 4 signings, 2 of which we've already got, ideally about 6-7 tbh. An understudy striker, LB, 2 CB's and a CM.
As for 3 at the back, our current squad is more suited to that IMO, yet Howe still insists on a back 4. So I don't see why he would buy players specifically for a formation he doesn't use.