cams and tpi tune

Went to a car meet in downtown orlando and found out a buddy of mine is selling a cam that he had in his car for about 2000 miles before he upgraded to something bigger. The cam specs are 209/217 .509/.517 112/59 <---(what is this lobe separation? He just wrote the spec on a paper real quick before i left) and hes selling it with some heavy springs for it for 50 bucks. But then some other guy said to not even mess with a cam that big because the car will be a horror to tune and wont even run right because its speed density. Now ive seen guys put in slightly bigger cams with the stock tune and it ran fine. I understand that in order to get optimum performance ill have to get everything tuned up but it shouldnt give me too much hassle. Whats the likelyhood that im gonna step into a world of hurt after putting a cam in this thing? The cam has about 2000 miles on it and with the springs ( I think he said lt4 springs) all for 50 dollars. I think its a great deal and will really wake things up in my engine, especially with the 1.6 rockers that ill have to put in to make it fit. Would I need to get new valve covers?And does anyone think that this cam might be too big and screw my gas mileage down to like....10mpg? I dont know but I though better to ask now then assume anything. Thanks for the help

lemme throw another question in there. do I need 7/16 or 3/8 stud rocker arms? Centerbolt? .150" offsets? etc.