I would say Gueye, Lookman and the Henry chap on loan were possibly the type Walsh and the scouting network pickup but the established players must have been more Koemans buys. I would love to know what players they have disagreed on, and what power each has. I would imagine Koeman can veto Walsh's advice on a signing but not vice Versa.
As you did the younger players and the likes of Sandro are Walsh type signings.
Klassen Rooney Keane Pickford Siggy were Koemans signings as well as the obvious CuCu and Steks