Technically NATO is already 'at their doorstep'. Norway, Estonia, and Latvia share a border with mainland Russia (with Estonia and Latvia being much closer to Moscow than Ukraine is), and Lithuania and Poland also directly border Kaliningrad, which is Russian territory, and Romania, Bulgaria, and Turkey only have the Black Sea separating them.
Yes, but only technically. What matters is the advanced weapons system each of these countries has on its territory. Think Aegis Ashore and the likes of that. Otherwise, they're just empty land (from a military viewpoint).
