Can one have two pending I-485s?

In prior years, it was not allowed, but now it appears they happy to accept your filing fees.

Yes, you can. However, if one of them is approved, the remaining one will be dismissed by the USCIS.

Not necessarily. Although you may consider transferring the basis of an adjustment application from an EB-5 category to an EB-2 category if all requirements are met. It might allow you to save on filing fees and to recapture some time during which the first I-485 was processing. Consult with an immigration attorney regarding your options.

The answer is mostly likely OK. It depends on whether or not you have maintained your NIV status.

I-485 cases can actually be transferred.

If the EB-2 is more faster and more favorable, what the employer can do is just request the I-140 be linked to your pending I-485 in EB-5. There is no need to file a brand new I-485.

It seems unnecessary to file twice, but there is no rule against it, and it should not cause RFE''s unless the applications contradict each other (for example, one says you are a policeman, the other says you are an aerospace engineer).