Yes, sure. Its just usually not a good idea (since tacs are poor defenders and are usually being lost without replacement, they need another source of fighters to shine).
Little more clarification on #4–when you liberate a capital (lets use Paris), all of the territory that the allies recaptured from the Axis immediately become French again, blowing off the other Allied markers and all going “blue” except for land that the Axis was holding. So if we say that the Axis owned Southern France and Syria upon liberation, France’s new income at the end of that turn would be 15, but there would be no building or placement of units until the next round (if they live that long).
As you probably read, the Allies can only “liberate” other Allied land if it has been taken by the Axis first. The only exception to this is the Dutch territory, and if you read the rules carefully, only ANZAC and UK can activate these, USA cannot. However, in another twist, all Allied planes can land on these whether they are activated or not.
In practice what this means is that taking Moscow or Paris back just tosses a ton of money back into Axis hands, while taking away the income from USA and UK (primarily) that they fought so hard to liberate. This creates a problem, because the Allies will actively avoid liberating capitals and handing so much cash to the Axis since in most cases, the Axis can easily recapture the key capital zones and control of it would just trade back and forth.
As a result, one sort of universally accepted house rule is to destroy the money rather than give it to the capturing player, after the first capture.
The Allies rarely benefit from capturing a capital, because the Italy economy is usually decimated before the Allies invade, and if you were able to capture Berlin or Tokyo, that’s usually endgame for the Axis if they don’t want to fight on.