1,Also, you can renew your EAD year by year until you get or not get your GC.So, you do not need to worry about your 6 years expired. From theory, once you are pending 485, you will get a chance to stay in America forever becasue you will give year by year to wait for your GC. If you will not get GC, it means America will not need you. I am not sure how long you will go back to home country then get another 6 years. Becasue it rarely happened. Once it happened, it may affect you to get new h1b visa for next 6 years.
3.No matter whether you get degree or not because you have degree already.