Is the expectation we will sign a specialist player to cover for every position? we might be but I'd be surprised given that to cover for 4th choice center back and second or third choice left back would make 2 additions, therefore if we are signing someone who can cover both spots you'd want someone that can do a serviceable job in both rather than world class at both; if he's a centre back then I'd want someone who is good in the air (which Kelly is), if he is good at dribbling and can put in a decent cross (which he can) then perhaps that is good enough for left back, I haven't seen enough evidence to suggest his passing is abysmal, playing in a team that's relegated can make even very good players look poor, Gini and Robertson were not earning rave reviews at their respective clubs either.
So in short, whoever we sign will be joining to cover first and foremost, if the player can cover 2 positions then we can have more options on the bench/in the squad to make changes and in general Klopp favours having a smaller squad which lends itself to this type of approach
This is probably unlikely to be the case
If he is a CB, that can only do a reasonable job at lb, then he probably wouldn't play at lb ahead of Milner, maybe even williams
If he is a lb, that can only do a reasonable job at cb, then he probably wouldn't play at cb ahead of fabinho or one of our youngsters.
In either case he is very unlikely to break into the 1st team, so you are better off persisting with the existing options in the squad. Any cb/lb that we sign is likely to end up a waste of transfer fee/wages and opportunities for existing youth prospects. Better off saving money for a front 3 signing, failing that I'd rather we sign no one