Do you have anything to use now? Use that to get started... fill in the holes where you need it with a line trimmer, blower, etc. I'm assuming you've got a functioning lawn mower at this point.
If you can start in your neighborhood - or one nearby, that's a good place to start.
Keep your costs as low as possible by not investing heavily in new equipment unless you're prepared to start running a 9 month a year operation, even while you goto school. If you're just mowing in the summertime and then leaving customers to fend for themeselve in spring and fall - my recommendation would be to travel light.
Lawn Lad, Inc.