My I-94 expires in exactly 30 days. Can I still file for an extension?

You do not need to file an affidavit of support application. You are always allowed to file I-539 yourself but in your case, I strongly suggest...

Yes, you can. The I-551 stamp in your passport serves to prove your status.

Can I fly outside the US while applying for permanent resident?

Unless you were changing status from a dual-intent visa, you need to start over with your Green Card application.

Green Card Application: US Spouse (Sponsor) between jobs, Can I show my income for financial support?

1. Yes, The beneficiary's lawful income can be used. 2. Yes, a permanent resident can act as a joint sponsor.

F1 TO H1B

If you change your job, this employer can no longer be your sponsor for the current H1B application and they will most likely withdraw their petition.

2 RFEs for O1-B visa - good sign?

You are correct. As a general rule, if you had not satisfied the other categories, the USCIS officer would include an explanation of why you did...