Maybe i should just keep McGregor for a season then.
Probably your best bet. If anything, target one of the younger keepers and give them a few matches here and there. After considering buying a clear upgrade (lack of money, wage room, and club reputation made that pretty much a no go), I ended up signing Rossbach in my save. I had him on a previous Vitesse save, where he started out a clear step below my starter and ended up on level with my #1 after one season. You can also watch for high quality regens, as you can find players at Prem-quality by 17 or 18 years old.
Its really hard to find a clear upgrade from McGregor without having more money, wages, and reputation to play with. And McGregor isn't likely to be the weakest spot on your squad.
Where else do you think i should improve the squad?
It really depends on what you want to do tactically, etc.
Playing a 4-3-3 (or 4-1-2-2-1 if you prefer), I targeted the right side of the squad. Particularly rightback. I signed Pavel Kaderabek, who is an excellent attacking rightback (though a bit limited defensively) and my primary "big" addition to the squad. Expected him to be my only signing that would start immediately. I wanted to sign a developmental right winger but whiffed on my targets for that. Ben Arfa is adequate but just on loan, plus I dislike his mentals and attitude. Turns out that Sagbo and Snodgrass are solid there, so more than covered. I also wanted a more creative central mid, as the current crop are solid but more all-around talents. Whiffed there as well, as I landed three developmental players instead of an immediate starter - Simon Gustafsson, Lewis Macleod, and Humam Tariq, with the latter needing a Work Permit. I focused on youth & depth rather than more immediately starters - the money can only stretch so far. I wasn't intending to, but sold James Chester to Souhamton and got Eder Alvarez Balanta as a replacement, with money left over for a couple of defensive depth players.
Outside of righback, there isn't any overriding immediate need positions. And even at RB, Elmohamady likely performs to an adequate level. Its an aspect that makes Hull an interesting save, because there really aren't any "untouchable" players in the squad. The closest are probably Abel Hernandez and Andy Robertson, and both will develop if you give them matches. Ince might as well. Most of the squad is similar to McGregor - adequate, decent, not an outright weakness, but yet replaceable if you can afford to. Having some money (and success, which is also key to getting money lol) will allow you to reshape the squad quite a bit.