How can I file an EB-2 case if I already hold an EB-5-based conditional green card?

Yes, you can file an E-2. However, because you are currently a conditional permanent resident, you may encounter an opposition from the USCIS just because an individual is not qualified to have two permanent statuses at the same time. Thus, be ready to give up your EB-5 conditional green card if ever the E-2 is approved since you cannot be on two permanent resident statuses at the same time.

You may apply for the EB-2 green card, but you will be required to surrender your current conditional green card before you may be approved for EB-2 green card.

Yes, you can still opt to have an EB-2 processing started by your employer and when that is approved for the last step (adjustment of status), you would have to withdraw your permanent resident status that you obtained through EB-5 and then adjust through the EB-2. Timing will be important and careful consideration regarding your options (i.e., EB-5 viability vs. EB-2 processing, exit strategy from your EB-5 investment, etc).

Yes, you can. If you are afraid that your conditional green card is at jeopardy you could certainly apply for the EB-2 through your current employer. You should be careful with this, though. It does not mean that your I-829 removal of conditions will necessarily be rejected just because the project or the regional center could be having problems. As long as the requisite jobs are deemed to have been created, chances are quite good that your conditional green card would become permanent. Of course, it is also possible that the project has serious issues due to fraud or simply market conditions in which case requisite jobs might not have been created and as a result, USCIS could end up denying your I-829 petition. If that happens, your EB-2 application would be the route you pursue. If your EB-2 petition is approved even before you file for I-829 you could withdraw your EB-5 petition altogether.

Your employer, while it may not be necessary, can file an EB-2 petition on your behalf. The petition itself can still be adjudicated, even though you are a conditional permanent resident, based upon your approved EB-5 petition on Form I-526, you could do so as insurance. Even though there are issues with the project in a regional center, that does not necessarily mean that your I-829 petition cannot be approved, and you would want to pursue that as well.

Yes, but before that can be finally approved you would need to abandon your current green card.

You can file for your EB-2 if you are eligible. I do not see any restrictions.

Yes, an EB-5 conditional resident can apply for an EB-2 or any other category, but you will have to surrender the conditional green card and apply for a new green card abroad when it is ready for final interview.

As long as you are eligible, you are able to have multiple petitions pending at once, including EB-2 and EB-5.