Hi, Yes you could change your name on your greencard if you provide a final judgment of the divorce showing that the judge has granted your change of name back to your maiden name after the divorce.....
And as far as becoming a US citizen, if you divorce you will have to wait the 5 years. Remember you could submit your application 3 months before the 5th year anniversary.
Yes, if you feel the need to change your name on your green card, you can request that it be changed by submitting a specific form with supporting documentation.
And yes, you will now be subject to the 5 year period as opposed to the 3 year period.