I still think messi as an AM might not work that great for us with the current set of players, first we need two holding midfielders who are physically strong and also good with ball. Masch can play there few matches maybe but we still need two more players to sign. Impossible imo, second if messi occupies center role too much Neymar cutting into middle and suarez occupying middle role up front is not going to be that effective. Play at RW and drop into middle is still the best solution I think but lets see what Valverde decides.
Early rumors suggest we might be in the market for Herrara, but that might just be second guessing from "Journalists" with valverde being our coach, Laporte rumors are also inevitable.
Edit: Above posts already discussing Herrara, did not see that. I don't think he will come anyway unless United sign another midfielder and deem him surplus to the squad.
Messi should play as a second CF, just a more technical CF behind a true 9, so that we can utilize his goal scoring abilities better now that he is aging.
Get a RW who can defend, to reduce the burden on the two pivots, typically a RWB (good both defensively and in attack). Vidal can play there. This way we leave Messi uptop with Suarez to do damage infront of goal just like how Monaco do with Mbappe and Falcao
Messi will not play RW, he played there half a season and came back, and trust me he will not return there and we don't have an Alves in our team or in the market to hold the wing by himself. Let's not deceive ourselves that somehow there is a WC fullback available who will click with Messi and make him return to RW.
IMO Masche does not fit the pivot role with Busquets. For that role, we need a more dynamic, sharp midfielder like Herrera, Nainngolan and the likes but younger. If he would come that will be great.