We need AT LEAST 3 new players IMO.
This is my realistic (apart from Di Maria) first 11 after we've got in new players:
------------------ De Gea ------------------
Rafael ------ Jones ------ Rojo ------- Shaw
------------ Herrera --- Blind ---------------
------------------ Mata --------------------
--- Januzaj ------------------- Di Maria ----
----------------- Rooney ------------------
I'd be very very happy with that, and it's strong enough to finish top 4 if we swap Rooney for RVP and vice versa. Van Gaal has already said he prefers the 4-3-3 formation the most.