There’s a big difference between Ron Paul stumbling his way into the White House vs. the Republican Party adopting his philosophy wholesale. I imagine he’d get next to nothing done - there are compromises he could make to whittle down Social Security or Medicare, but he is not a big compromise guy. He could use his Presidential powers to draw down the global reach of the US military. He could do other stuff as well, but I don’t imagine he’s going to want to push Presidential powers he thinks are illegitimate.
Gridlock in Congress as they won’t write bills he likes and he vetos most of what they do. Economy in the trash with no support, stimulus, or direction. Large numbers of decommissioned soldiers with no career prospects out in the streets.