If you filter the oil (the battery pumps work OK - cheese cloth would better but I don't use it either) and stay around 350 you could get 4-5 turkeys out of a batch of oil -- maybe more.
I usually rotate one bottle of oil (1.25 gallons) every go around. But, I got three fries out of the first batch. The older oil will give you a nicer brown on the skin but if it's too old it'll darken the bird before it's done.
I've been using canola because I'm too cheap to buy peanut oil :D
I don't think you can go bigger than a 12 lb bird to fit in the fryer.
It depends on the size of your pot but generally 12-13 pounds is a big as you should go. I think the rule is you only want the oil to come up 2/3 the depth of your pot with the bird in it -- otherwise you could get boil over (not pretty -- don't ask, I know this!!).
Southern Brethren BBQ Competition Team
"It's all about getting paid!" - Myron Mixon
"I love being hated in my hometown!" - David Hair
KingFisher Gator Rotisserie cooker, WSM, Stainless 5 burner with IR gas grill, Turkey Fryer, Weber JD Commemorative grill, slightly used Bandera chamber for future use as a cold smoker, Masterbuilt 40" insulated ELECTRIC smoker