H1B Perm/Maxout

  1. Can I enter the US if passport expires in less than 6 months?
  2. Also, if my passport expires in Feb mid and valid H1B till Feb end. Does it affect anyway?
  3. Another question - Example - If I have my H1b valid till Feb end and my max out is also in Feb end as well. If I do international travel for 3-4 weeks and come back, can I apply H1B extension for the vacation period taken (3-4 weeks). This would also push my max out date from Feb end to Mar/Apr based on the vacation period.
  4. What would happen if I reach max out when PERM is pending? for example - if max out is in Feb end and my perm is getting approved in Mar and I-140 getting approved in Apr, then If I get the stamping in May , Can I enter US again in May or do I need to wait for 365 days and come back?

Thank you in advance!