Manchester United's striker shortage is not a big problem right now, I think. Rashford can be considered for that area. If they can get Harry Kane it would be a nice extra deal but I can't imagine Tottenham selling him to a competitor. So I think this possibility is slim. But Hojlund will strengthen them, that's for sure.
Rashford isn't so good in the central attacking position, he is better on the left side of attack, and Erik ten hag would know that if he wants to harness the full potential of his best attacker, he'd have to play him in his favorite position.
Having said that, Harry Kane doesn't seem to be serious about leaving Spurs, if he is; he would have handed in a transfer request, other than that, it would be impossible for Manchester United to try and reach an agreement with Spurs/Daniel Levy for Harry Kane. I don't know much about Hojlund, but i think Atalanta are asking for too much for the Danish international, if they don't reduce their valuation of the striker, Manchester United might be forced to walk away from the deal.