Largely not. The large-scale consensus, Soviet industrial output, GDP, GDP-per-head, and GNP had returned to pre-war levels by 1948. Soviet agriculture production had returned to pre-war levels by the early-50s. And the last economic damage, in the service sector, had been repaired by 1955. Of course, in some ways (such as demographically) the USSR never really recovered by WW2 and this had it's own distorting effect on it's economy, but to pretend that the USSR didn't grow at all from the pre-war level is downright farcical.
No, that's completely bogus. The Maginot Line was a huge waste that came at the expense of the rest of the French Army and extending it to the coast would have diverted so many resources as to leave the French army so weak that the Germans would have wrecked their face, line or no. The experience in WW2 showed that fixed fortifications by themselves are worthless. They need a large effective army to back them up. Of your examples, the Mannerheim line didn't exist in WW2 (that was WW1) and the German defense across the Italian peninsula were ad-hoc affairs relying mostly on field fortifications and terrain without the massive investment of fortress-like fixed fortifications akin to the Maginot Line and even there they were consistently (if slowly) pushed back. While there are examples of positions relying on fixed fortification holding out in WWII, those defenses usually relied on the attacker being at the end of their rope. Without that, the norm was for defenders to delay the attacker for a bit and then be defeated, usually taking heavier losses in the process as the attacker battered them down with firepower.
Even had the Germans attacked the Maginot IOTL head on, they probably would have punched through it and overrun the French frontier before exhausting themselves and bogging themselves against the increasing numbers of deploying French reserves on a rather narrow front over difficult terrain. It would still be a victory for them, just not the "knock France out in one-blow" victory that they needed.
The most successful defenses in WW2 were those which relied on aggressive maneuver by mobile forces supported by (and not the other way around) counter-penetration forces operating from quickly set-up field fortifications enhanced with obstacles like mines. Which is precisely the sort of defense the Soviets planned to mount in the eventuality they were ever attacked first.
What's more, the disposition of Soviet forces throughout the Cold War was actually much better suited to such a defense then their enemies. Soviet armies were echeloned in depth, actually gave them much greater defense-in-depth then that which existed on the NATO side of the border. NATO's commitment to forward defense makes little military sense unless they were to take the offensive and this formed much of the basis for Soviet justifications of fears of a sudden NATO surprise offensive. Not to say that the Soviets were in the right or anything, but to try and argue the Soviets perceived no threat from the West is boulder-dash, even before we factor in that they were at a disadvantage in the nuclear angle for the first half of the Cold War. The Cold War was very much a case of both sides having genuine mutual fears of the other, even if those fears do not necessarily justify their subsequent actions.