Some notes:
In the world in which we do nothing but retain players, trade Jimmy G, and just draft, subtracting Jimmy's cap hit gets us to $7 under the cap and 9 players short of 45. Adding four draft classes gets you over the cap again. Someone has to go.
The only O-line under contract are Solder, Cannon, Devey and Kline, who are around $20.6 million combined. The current entire O-line including backups are around $17.7 million.
The D-line consists of Chandler Jones. Sealver Siliga, Easley, and Chris Jones, who are around $17.5 million combined ($15.5 million of which are Chandler Jones). The current D-line including backups is $17.1 million (11 players)
Malcolm Butler's cap # is $6 million for 2018, goes to $13+ million for 2019 and 2020.
The LBs consist of Hightower, Collins, and Deontae Skinner, who are around 21 million. Current LB's are $14 million for five players.
Assuming draft capital is used to draft OL, DL, and LBs, we still need to shore up the offensive skill positions. The RBs are Blount and two pass catching backs. The #2 TE is Hooman.
Please remember in this world Belichick is not a significantly better drafter than he currently is.