You seem to be saying two different things. I agree that you might as well borrow as much as you can (which is as you say is limited by your EFC and your annual school budget) since the rates are low and you can make more than that in the market . However, then you say you will take money out of your IRA to pay the interest. This is a very bad idea and is a triple whammy against you: 1) you will defeat the idea that the rates are lower than you can make in the market. By pulling the money out of the market to pay the low interest you are not making money in the market. 2) IRA money (if it is a traditional IRA or from a SEP-IRA, 401(k), or 403(b)) is pre-tax money, therefore you will have to pay tax on that $500 (which if you made >$100k last year will be at the highest tax rate. 3) Unless you are older than 59-1/2 you will pay a penalty to withdraw money from your IRA.
Like you said, the interest rates right now are low (that could change...the interest rates on Stafford loans are variable) so it is better to borrow all that you can and let your money work for you in the market. If there comes a time when it seems the interest rate is higher than you can get in the market, then pay money into the loan.
Medloans is a good program but definitely compare with other lenders because some (T.H.E., and Access) tend to have better repayment options. Theoretically, it may be better to borrow with different lenders...you might have to deal with getting a few different things in the mail, but it makes for more options when consolidating later on. If all your money is with one lender, you have fewer options when consolidating.