khurram,
You should download IRS publication 519 from https://www.irs.gov/pub/irs-pdf/p519.pdf and turn to page 9 where the topic of a nonresident spouse being treated as a resident is covered.
As to the W-7 timing, I have no idea. What I would suggest is to use TurboTax to compute how much you will owe, if anything, and if you owe, have TT print out an extension form for you to send in with the payment. This will then give you another six months to get the paperwork done and file your joint return.
