4 King studs or 4 Jack studs
1 king and one jack per side, assuming it's not an unusual load above. If your header has space above, make the jack continue up to the plate. 

Only caution is that even though the 6" fill looks good on paper, the slightest fatness in your framing materials coupled with a tiny bit of "out of plumb", might mean your door is a tight fit. Buy the dryest 2x material you can find.