I presume you are referring to Multivariate Calculus. This is a good choice. It will really give you a taste of the intensity you will be facing in an engineering curriculum. Congratulations on your admission to Iowa and Purdue. Hopefully they can give you a financial aid package that will give you choices about where to go. I am not sure about whether there are any official deadlines for your decision as there are for entering Freshmen but you definitely need to take your time and find the best combination of finances and curriculum for you.