Check with your school's financial aid office and they should be able to help you with the questions on how the aid works. I know for me, when I was an undergrad I received my stafford loans it was in two lump sums, at the beginning of each semester and it was paid directly to my school's student account.
As for your question on whether it makes sense to contribute to your Roth IRA while taking out loans i guess that depends on what kinds of numbers we are talking about here and what other debts you may have, if any and what your expenses are, what other savings you have, etc.
Personally, I would probably look at trying to take out the least amount of debt possible and ignore the roth contributions but you could certainly make an argument and run some numbers where doing the Roth contributions will work out in your favor, just for me personally, owing less now and not having to fight for returns against the interest you'd be borrowing makes more sense to me. I would also rather have 10 - 15k in regular money savings that I could access for any unexpected needs after 2-3 years of grad school rather than 10-15k in a roth account, so I would say if you don't have current savings bucket start filling that first
Remember you can make payments at anytime to your student loans, even while in school so you don't have to take the maximum that they approve you for and / or if you find out you don't need all of the loan you can pay a chunck back too.