Your I-485 receipt is sufficient to apply for and attend college; you don't need to wait for the EAD.
But for Federal financial aid you'll need to wait until you have a green card, unless you already have asylee or refugee status.
And to be eligible for the in-state tuition rate, most states require you to have a legal status (other than F-1 or J-1) for at least a year while living in the state before you can qualify; getting a green card doesn't immediately qualify you for the in-state rate. The time you spent with a pending I-485 normally will count towards that year.
