JHU CTY is option for online advanced math. My older son did this his senior year for MVC since his school math curriculum ended with AP Calc BC. Can’t say it was the best designed course but the experience was good. He was ahead of many of his peers when he got to Wharton.
Outside merit scholarships can be nice, but look deeply into how specific schools handle this. Many colleges (not all) will take that scholarship money and just reduce your financial aid package - leaving you a net gain of nearly $0.