H1B to F1- what happens to my H1B when I apply for F1


I am on H1B visa since 1st October 2013, I have my PERM applied and hoping to get my I-140s approved by next 6 months. I am applying for B-schools in US and planning to start school in Fall 2015

My questions are the following:

  1. Once I apply for F1, what happens to my H1B. I will have 4 years remaining out of my 6 year validity. Will they cancel my H1B?

  2. After the completion of my course, can I change back to the same H1B and use the remaining 4 years? Or do I have to apply for new H1B, fresh through Quota/Lottery? I understand, my maxout clock will not be reset and if I get to continue with H1B, I can only stay for 4 years. But will that be a fresh H1B through lottery or I can retain the old petition/stamp and just transfer it.

  3. What happens to my approved I140s? Can I retain the priority date? I understand that my I140 is linked to my social security, so it is the discretion of the USCIS officer to grant me retain the priority date or not.

Please help me with my queries, I need to start with my GMAT Prep and applications, if only, I do not lose my current H1B.