We have Dumba + Spurgeon for next season, and then Lambos, Hunt and O'Rourke coming up. One of them can play off-hand. Merill is also signed long term. Next season, only Goligoski and Benn are up for contracts and then Dumba and Kulikov after that. Getting a depth defenseman isn't going to be that hard. More so, Addison hasn't been able to break into the lineup that has consisted of Benn and Merrill.
As for the 4th liner; we're already have trouble finding a regular spot for Dewar, who is up for a contract at the end of this season. Keep Duhaime, keep Sturm mix in Shaw, Giroux, and McBain (if we sign). Not to mention Pillar will need to be signed, along with Hentges.
It's a late 1st, a RFA, a B prospect in Addison and a 5th. I don't consider that breaking the bank.
My concern is going to be a 1st, 3rd and a prospect like O'Rourke or Khus.