--Yes, you can try, but it is not very strong case in Eb1a.
2. if i file eb1a, should i file i-140 together with I-485 etc? (i'm planning to file eb2/NIW like 1-3 months after eb1a)
--yes
3. if i file two i-140 petitions, and the one under eb1a is denied or approved later than the one under eb2/niw, can i use the I-485 petition under eb1a for eb2/niw?
--both 140s approved, you can change 485 from one 140 to another 140. But you can file two 485.
4. why post-doc or researcher/professor doesn't file eb1b? is it because it requires permament employment letter? what is the difference between eb1a and eb1b?
--post-doc or researcher/professor is not permament employment.
--Eb1a apply by your self, requres 3 from 9 evidences,
eb1b apply by employer, requres 2 of 9 evidences