522 will make more torque and at a lower rpm. If you can swing it I would go for it.
Fuel consumption, all else being equal (cam, heads, intake) mpg will be close, maybe 2mpg difference. But usually with a stroker comes a bigger cam, quite possibly better flowing heads and more fuel being blown out the tail pipe.
For a given cam, a 522 will make more vacuum than a 440.
I would run headers, they make more power, size would be dictated by your cam/head choices. For a 440 I would probably do 1-7/8 tubes and 2" for the 522. You can run manifolds but you will give up some power and cam choices to run best with manifolds are much more sensitive.
For a street cruiser rag top challenger, a stock stroke 440 will make all the power you want, but if the cost difference is close why not spring for the extra cubes!