I'm confused – Why wouldn't Apple pay you directly?

You shouldn't have to ask for anything, they should present you with an offer.

Meanwhile, you should do appropriate due diligence and interview with other companies that interest you and see what other offers you get. If Apple is interested in hiring you, no doubt other companies will be too.

Also: keep in mind that relocating will incur at least a few thousand dollars in expenses (which your future employer should cover as part of the comp package) and that living in the bay area is very expensive. 50k is do-able, but won't take you very far.