potential problem

it's unlikely you can get F1 student visa, because you already showed your immigration intent via I-140/I-485 filing while F1 is for non-immigrant purpose.

but i'm not quite sure about whether holding EAD w/ I-485 pending would give you the freedom to quit your job, especially if your GC application is employment based. i'm curious to find out. once we have a clear answer, i can add it to the Immigration Wiki at http://www.road2usa.com/gc/wiki.php so that other folks can have a reference in the future.