AP and EAD question

I have already ted my I-485 and AP, but didn't file EAD at that time. Now I plan to go back to China this winter.My qestions are:

1. Is it safe for me to use AP without EAD?

2. If I file EAD now,I will only need the form I-756 and 485 receipt,right? Any other documents necessary for EAD application?

3. Can I file it by myself online?

I know that is a lot of questions...Thanks a lot!