The Bush Tax Cuts were passed to save us from a GOP-projected future in which the entire national debt would have been paid off by 2015.
And yes, it would appear that they were successful.

It lowered taxes by 3% on the top income tax bracket. Other brackets received different amounts of cuts.
Dunno about "helped". I'm pretty certain that 401K's existed before Bush, and were completely tax exempt before him. But it wouldn't surprise me if he didn't adjust them in some way or another.
Nope. Created in 1997.
The amount that you are allowed to put in them has been increased several times. Don't know if it was in the same law as the tax cuts or not. Might well have been.
As is typically the case, I have no clue what you're talking about, here.