485 pending=AOS

1，进入AOS非得使用EAD不可吗？或者说只要485pending就算AOS？
AOS, once you file 485.

2，如果H1b到期而工卡还没批下来，肯定不能工作，但应该算合法吧？不会影响485吧？
You can stay legally, as AOS is your background status.

3，如果H1b到期但新的工作还没找到会有问题吗（eb1a)？

Then you will only need to worry about RFE from CIS for paystub or Employment verification letter.