Woo, that's some loaded questions. I'll take a stab at it, but part of it may be more generic than you might be asking.
IMO, it's difficult to label a person as knightly, but much easier to label an action as knightly.
Robbing from the rich and giving to the poor? Too broad, it would be, to me, circumstantial on whether or not the rich person is deserving of having some or all of their wealth removed. To be truly knightly, I'd have to label it as "robbing from the corrupt and giving to the needy".
Whether he is alone, or has a few men, or an army of thousands at his disposal, is of little consequence. Standing up against oppression is the important factor to being knightly or knavely.
As an example, if someone had traveled from village to village, scamming the citizens, and became wealthy by it, they deserve to have it stripped from them. On the other hand, if someone traveled from village to village, selling wares or performing odd jobs and was able to save and become wealthy through honorable means, I think they are entitled to keep it. In taking from the rich and giving to the poor, one's view of good or bad generally depends on which side of that fence they are on, and if they would benefit or be adversely affected by it.
The manner in which it's taken ... frontal assault, or by deception? The intent is as important as, or perhaps even more important, than the method. As touched on in another thread, Edward of Woodstock (the Black Prince) had an unconventional method of warfare in attacking the weak spots, and avoiding the strong defenses - but was that cowardice? Was that strategy? Was that bullying? Would it have been better to attack the strongest points head on, and potentially lose the war? Which was the more chivalrous, more knightly, path?
Labeling a person as knightly, to me, is a measure of multiple actions - are they more knightly than not? Do their falterings outweigh the good things they do?
Drawing the line of knightly and chivalrous is akin to trying to hit a moving target; it will constantly have a gray area that will shift around based on varying circumstances.