To be honest, I don't have much information about this club. however, it seems that Xabi has the potential to bring Leverkusen to become one of the teams that can become a competitor in the top 4 of the Bundesliga next season. moreover, if he gains support by bringing in some potential newcomers.
As far as I know, only Xhaka wants to be brought in by Leverkusen. although there is no certainty, but the contract has been sealed if Arsenal get a replacement. for other newcomers, I don't really know it. apart from that, if Xabi Alonso continues to carry the playing style of the system that he applies. Xabi needs some ideal new additions, I mean potential players. thus, Leverkusen can compete competitively at the Europa League and Bundesliga levels. at least, Leverkusen has the chance to finish in the top 4 of the standings. but with the condition that I said before, he needs some ammunition to strengthen the depth of his team.
Leverkusen has been receiving financial support from Bayer the pharmaceutical producer for a long while now. That is why they could afford above average salaries and they are also a team that is popular by young players who want a club where they can play and develop further and then take the next step. For Xabi Alonso these are good conditions as it seems that he has a good connection with younger talents and at the same time he can build a quality team since they don't have to let all the talented players go every year. Years ago Leverkusen has been a strong rival for the top four and I think Alonso can get them there.