You've got to try to bridge Tony for 2 years, he won't accept 3 but a decent raise likely means 2 years. This gives management the flexibility to see if he can repeat his scoring, if so then he's massively valuable in a hockey trade. If Lundqvist makes him expendable then oh well. Personally I'll take a two-way puck mover on an ELC than a 60 point D man who just isn't great in his own zone. Especially with Fox and Trouba already here, both of whom can play the pp. We'll see next year if Fox brakes 50 points, I think he will and we also know Trouba is capable 40+ while playing big pk minutes as well. But we have a season or two to watch the righty D spots play out.
Regarding left D, I would try to plug a hole there now with an under radar pickup like a Haydn Fleury. Someone who will be cost-effective, gives the lefty prospects time to develop in the minors and who still has some boom potential. He's a young vet already and come 2021-22 when Smith and Staal are off the books, can handle top4 duty without forcing someone like Miller or Hajek into minutes they shouldn't handle.
I'd just be super careful and not move any of the top prospects, and not give out long term contracts to players you see a possibly replaceable within 2-3 years. This team is not 1 or 2 moves away from competing, so let young players gain the experience. Let the really young guys develop overseas or in junior. Continue to capitalize on value of older players who need contracts, be it Fast, Strome or Ada.