That is good to focus on transfer period for Bayer Leverkusen especially after their amazing undefeated win in 2023-2024 Bundesliga season because successful teams mostly face challenge of their best players getting big offers from other clubs which makes transfer window very important time. Your point about needing to bring in good young players to replace anyone who leaves is spot on as their ability to stay in championship race next year will depend heavily on making smart new signings. If they can not replace key players well it will be hard to repeat their success.
The structure of Bayer Leverkusen next year is very, very important. They will play with a new coach and the players will need to be in harmony with him. They should complete the transfers quickly so that the new transfers can contribute well to the team. Their return to the championship in Germany depends only on perfect planning.
Bayer Leverkusen will build their squad next season, although I understand that they will sell some of their players during the transfer window, but they are going to get new players to strengthen their team again. They will be starting the new season with a new coach. With this season, I think they should get in new players early so the new players and the current players will be able to get used to the coach's style of play.
Let's's see what Leverkusen will do during the transfer window, but I know they will definitely strengthen the squad ahead of next season;; they want to repeat their success again next season..