My present employment was terminated on May22,09. I-94 has the data of 25 Sept 2011. I applied I-539 for COS to F-1 as I was already pursuing PhD before converting to H1B and am in my last phase of doctoral degree. The university is also willing to offer me assistantship for starting summer quarter and I-20 in I-539 has starting date of June 22.

I have following questions:

1. Can I stay in US while I-539 is pending?
2. Can I start attending university full-time while I-539 is pending?
3. Can I accept assistantship (research or teaching) while I-539 is pending?
4. If I accept assistantship and the application is denied than do I have to immediately leave and re-apply from home country?
5. If I find another employer to sponsor my H1B than do I simply have to withdraw my I-539?