For now Kovacic is the only transfer made by Manchester City this summer. However they have been working on completing a way bigger deal for a long time. They are after Gvardiol as you know and their latest offer was really close to the amount Leipzig wanted for him. I still don't see any update on these negotiations but I assume Manchester City wouldn't stop until securing the deal.
City is still having rodri. Gvardiol has become one of the most important target by manchester city. The talk is still ongoing and you can expect the news to come in upcoming days.
As long as city will agree to pay the fees and gvardiol will be moving to the manchester city as soon as possible. it's a just matter of time.
Rodri and Kovacic are players who can play in the same position of course. But their main positions are different. While Rodri is more of a defensive midfielder Kovacic is playing at the centre. Both of them have played in their natural positions most of the time so far. But Guardiola can still make changes between them when there is such need of course.
The aim with bringing Kovacic was rather filling Gundogan's place after his departure. I think Kovacic is a decent choice for that. I don't know if he would be a long-term signing even though the contract is until 2027. It depends on his effort otherwise Manchester City can simply send him as well.