You can attend school full time even on H4. The only advantage in having EAD is , you are eligible to receive stipend like teaching assistanship (TA) or research assistantship (RA).
On h4, you are not allowed to recieve stipend, but you are eligible to recieve tuition waiver. On H4, you are not allowed to earn money like TA, Ra, but you can get tuition waiver.
iF YOU have a sponsor who would pay for your tuition, then I am not sure how exactly it works when you are on EAD. You might need some more investigation here.