When one combine the players that won't fit into ETH system (AWB, Maguire, McT and co), the players who will leave (Mata, Matic, Pogba, Lingard, Cavani, Periera and co) and the players who are too injury prone to be relied upon (Varane, Bailly, Jones and co) then I believe that we'll need at least 6-7 players to strengthen the side. My choice would be
CB: Timber (45m) and Rudiger (free)
LB: Tagliafico (free)
DM: Kamara (free) and Alvarez (30m): With Matic gone we basically have no DM. Alvarez know ETH system inside out while Kamara has great potential and is on free.
MC: Ruben Neves (35m)
STK: Nkunku (70m). I know he's more comfortable as AMC but he'll do well as a false 9, adding more bodies in midfield that we need. Nkunku can also play as RW, AMC and LW giving us options.
Estimated expenditure would be 170m which would drop thanks to us selling Henderson, Maguire, Shaw McT, Periera and hopefully Martial and Bailly as well.
GK: DDG, Heaton, some random kid
RB: AWB, Dalot, Laird
LB; Tagliafico, Telles
CB; Rudiger, Timber, Varane, Lindelof
DM: Kamara, Alvarez
MC: Neves, Fred
AMC: Bruno, VDB
AMR: Sancho, Greenwood
AML: Rashford, Elanga
STK: Nkunku, Ronaldo