The US would not go to war over Estonia but it has nothing to do with nuclear weapons. It just wouldn't be worth the death from a conventional ground war. Additionally Estonia would be kind of responsible for bringing it on themselves via terrible policies.
As to nuclear weapons, we spend too much time discussing them. Nuclear weapons do not deter military action at all. If Ukraine had kept their nukes, Russia would still have taken Crimea. The only thing nukes do is deter other people from using their own nukes.
1. Allowing a Russian occupation of parts of Estonia would jeopardize the credibility of NATO and all your other military alliances. The size and economic importance of Estonia doesnt matter in this context.
2. Do you have even a shred of evidence to back up that claim?
