Better keep your H1b until

your I140 is approved. If you use EAD and I140 is rejected, you are out of any status. Keep in mind that the rejection rate for 140 is much higher than 485's. After getting 140 approved, you will have a real "AOS" in which people are using EAD because the rejection rate of the 485 with an approved 140 is pretty low. But using AOS's EAD is still a risk which is not bigger than the convienence you get.