Slot confirmed and got slightly irritated at the suggestion he played 4-2-3-1 in Holland, so based on that alone, I'd go with a 4-3-3 formation. I expect few surprises, except perhaps giving the Copa America players some extra time to get up to speed in training or off the bench. Slot's dilemma is that Gakpo is the player most suited to the number 9 role in Holland, but he's also been shining recently as a left winger. That's a key decision for him to make.
I have a sneaky, optimistic feeling that Slot could have a really positive impact on Gakpo, similar to the way Klopp did with Firmino. There are some parallels in that the previous regime shuffled him around without a clear plan, despite him looking like a tidy player. Slot has the opportunity to correct that. The Dutch players might also get up to speed quicker if they played a similar style in their youth, but that might be a stretch. Anyway, it's an interesting aspect to keep an eye on this year.
For now, I'd stick Gakpo on the left, interchanging with Jota at the number 9 position. Elliott has been training longer than most, and I'd wager that Slot will like him and integrate him into the first eleven. Whether that's to the right or left of Endo is tougher to call. Both Elliott and Szoboszlai will prefer the right. The wildcard would be starting Bajcetic at 8 on the left side. A strong pre-season could open that up for him. The same could be said for Gravenberch, Jones, etc, so let's see. There's not much to go off at this stage, and we'll know more over the next month.
----------------------Alisson--
--Trent----Konate------VVD-------Robertson----
--------------------Endo-------------------------
--------Szobo---------------Elliott-------------
---Salah---------Jota------------Gakpo