how big is the pot? i use everything and anything.... buckits,folger coffee tubs, paint cans,etc etc (just make sure you rinse with hot water before adding soil).
when i started out growing mine i use the same kind of cups you used, after a week or so i then moved them to there permanent spot in pots (10" in width, 10" in length) i only have one plant per pot.(when you move them make sure you have a ball-sized clump of soil around your roots of the plants.(wear gloves too)
how big is your grow room? and how many plants are you plan on growing? what kind of lights do you have?