There is a strain of Orthodoxy theology/speculation which holds almost exactly what you have said. In fact I ascribe to it. We don't speak of purgatory but rather "the place of the dead" or "Hades". Its the place Christ descended to after the crucifixtion. The difference lies in what is going on. The West and the East differ as to what sin really is and in consequence of that, distinctions between mortal and venial sins are meaningless for us. The purifying process is a result or an effect of God's love an mercy. In this sense it is not about getting rid of minor sins, but rather about finishing the process of theosis. Some Orthodox, Kalomiros among them, have speculated that for those destined for heaven at the final judgment, that process is a joy because those souls react that way to God's love while the damned are tormented by that love.
These of course are speculations and nothing more. The only authoritative thing Orthodoxy says about that period between the particular and final judgments is that the soul can do nothing sua sponte to improve its lot, beyond that its all guesses. I will add, however, that the idea that that time or place is somehow or other expiatory is, while seen occassionally, outside the consensus patrum as we know it.
Definitely. It is often stressed by the Catholics, that the reason we pray for the soul sin purgatory is that they cannot any longer repent and liberate themselves.