Uh... how weird, I thought that reckless abandon scaled with BAB, not "levels".By RAW I'm not sure what does "level" refer to... does it mean exclusively your barbarian levels or your total character level? It's not quite clear.
On the Viking, it states that: "At 4th level, a Viking gains the rage ability as the barbarian class feature, but her barbarian level is considered to be her fighter level –3." There are no mentions of what happens if you take actual barbarian levels or levels on some other class with access to Rage.
So, you are considered to have a barbarian class level equal to your Viking levels -3. It doesn’t say to what they apply, but I think it’s safe to assume that it works for Rage powers, since they are closely related to the Rage feature. Apparently it's either A) You use your full character level to check for this bonus or B) You use your Viking level -3 plus whatever other levels on classes that have Rage (as it usually is with this kinds of things, like Animal Companions).
As an aside note, you get Barbarian rage at 4th level, but it replaces a class feature you get at 5th level. This all makes me think that this archetype wasn't all that well edited, although I must say that it is quite cool.
For your second question, I'll go with "They apply starting at 4th level, since barbarians also gain the Rage class feature BEFORE they get access to Rage Powers."
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