1. like any area in psychology, the program will be a great fit if you can find a professor whose research interests match your own. there are plenty of quant programs that are measurement focused (psychometrics) and more general quant programs that have professors who work in measurement and assessment.
2. i came into my program with no calculus (except AP in high school, but who remembers that?). they required that i take the calc sequence once there, but it wasn't a big deal that i didn't have it at entry.
3. coming up with new methods is really only one aspect of quant, but what you describe is much more applied than typical for quant research. my master's thesis (and a lot of quant work) involved testing the effect of violating an assumption on a specific type of analysis - this often uses simulated data, not real data.
4. i came in with very little experience on SAS or R. my program typically uses SAS, though a lot of students in other areas in the department use SPSS. that kind of learning experience would definitely be helpful, plus if you could get a letter of rec from a quant person, it would be a bonus.