I'll give answering your questions a crack....
1. The +1 category has "fired at by small arms" and "enemy moves within 6 inches", is that +1 only once or +1 for each occurrance? ex. being shot at 3 times (let's say no wounds) would that be +3 stress when they roll when activating?
That is +1 per each of the conditions listed. So yes, if a figure is fired at by small arms, and an enemy figure is within 6", that would be +2.
2. What does a "light wound" do to a figure?
It gives the lightly wounded (or "lightly injured") figure penalties on his shooting, hand-to-hand, and morale rolls, for example. These penalties are listed in the appropriate tables.
3. Units gain stress tokens from wounds and those are the only stress that carries over each activation, adding to any stress tokens acquired by actions like being shot at?
Yep. All of the accumulated stress markers (permanent or temporary) affect the morale roll. The difference is that you remove the temporary markers after your do the roll. The permanent markers are, well, permanent.
Does that help at all?