I currently work for a big company. I 140 approved and I-485 pending for more than 180+ days. This employer does not revoke/withdraw the I-140.
I plan to move to a newly funded startup company. Company was started 9 months back and they have 10 employees. They are operating on venture capital funding funding currently.

I have heard about legitimacy of employer issues coming up for small companies. What all documents must I keep handy to prove the legitimacy of employer....?

Will I be jeopardizing my green card application if I chose to move to such a small and new company. They don't even have tax filings since they are less that 1 year old. All they may have is audited financial documents regarding their funding. What other documents must I keep handy...?