Do you mean you want to work temporarily for some income becfore going to a PhD program? I am not quite sure what the "BIG TEN OFFER" means.

You can definitely start working as long as you have OPT, and it doesn't hurt to let your employer to apply H-1 for you, because you might change your mind after working for a while.

At the time you want to quit, it's very easy, the common industry practice is two weeks notice. Let your boss know two weeks before you leave, there will be no problem at all. You don't even have to tell the reason of quitting, but telling them you are going to a PhD program in top university will gain yourself a lot respect from them. You might also want to keep touch with your boss or coworkers because you may need them to givey you reference in future job hunting.