Can I borrow that wide paint brush when you're finished? I need to finish painting my house by tomorrow.
I agree with you that most libertarians are culturally "liberals" and many (especially the large-"L" Libertarians, and those at LewRockwell) are geopolitically naive, but it's grossly innaccurate to say that libertarians are "marginally Rightist on economic and governing matters." Libertarians do really believe in getting rid of 80% to 90% of government.
I, like I think most libertarians, believe that the only important functions of the federal government are maintaining the military and the criminal justice system (and a smaller criminal justice system at that, that leaves most such work to the states). Those 2 functions should amount to maybe 98% of federal expenditures and employees.
Libertarians do disagree on whether the current armed forces are of a suitable size (as I do), or whether we should become more isolationist and cut the armed forces as well. That question makes the difference between cutting total federal expenditures by about 75%-80%, or by 90%-95%.