Hi Alex!
I'm not very far on my investment journey (just finished grad school myself). I would strongly encourage you to take out the minimum in student loans possible. The only ones I would ever suggest you take out are subsidized staffords, and then I would take whatever money you can save by taking them out and sitting them in a *safe investment for the term of the graduate program and repaying as much as you can right before they start repayment.
This may sound harsh but unless you are only taking out subsidized staffords, IMHO, you should NOT be investing in anything other than an employer 401k and only to the match. You will get a better return on investment by not taking out those loans and accruing interest on them.
I know! I just got out with $140,000 in student loans from grad school. Mr. MEJG worked while I was in school, I worked during part of school, and we were frugal, by most standards, I got out with approximately 1/2 the loans that most of my classmates did. I completely regret the "little luxuries**" we allowed ourselves. I totally HATED not contributing to my Roth IRA while I was in school, but every penny you don't take out is money in your pocket.
If I were you I would seriously look at the numbers and consider cashing in any investments I had outside tax sheltered accounts and using that to reduce you loan burden.
My Roth is at vanguard and I am approximating this portfolio
http://www.marketwatch.com/lazyportfolio/portfolio/yale-u-portfolio I plan on rebalancing quarterly and sticking to the asset allocation. I'm learning more about DRIPs and will probably go this route with a taxable account when we get there.
BUT, I won't be investing anymore other than 401k to the match until my student loans are payed way way down at least, and probably not till they are payed off.
As to how it is passive income. If your investments increase by 7% a year then ~4% (3% assume inflation) then you can sell that 4% and live on it. In the case of dividends, you stop reinvesting the dividends and have them deposited in a bank account and spend those. So instead of putting money in, you are taking money out of your investments.
Sorry for the length, and the preachyness, this is what I wish someone had said to me instead of "you're doing great, you'll have a good income, and school debt is good debt"
*Safe meaning a savings account, CD or Bond - with a return that is worth it, so at inflation or HIGHER, so unless you have an AU savings account you're kinda SOL right now.
** A dog and cat we wanted desperately and love!, buying lunch as often as we did (not often), dinner out together and with friends, a kitchen gadget here and there, a new bed when we moved internationally, icecream and emergency chocolate, using the car when we could have biked etc. All things that were justifiable at the time.