[1966Stang]

Hi! I've come across a black 1966 Landau T-bird for sale ($5,000 obo) supposedly with a 428. I'd really appreciate some advice concerning whether or not to pursue the vehicle further. To be honest, I'm approaching this as an investment, not a car to be driven daily. From my initial phone conversation I have learned that it is in "original condition", interior is flawless (white), paint has some minor dings, no rust, sliding steering wheel (automatic) and has basically been sitting in a garage for 5 years with occasional start-ups but hardly no driving. The power windows don't work (blown fuse but can't find the fuse) and it leaks oil REALLY bad, but does not know from where. He says that it looks like it's coming from the oil pan. I've seen pictures of the car inside and out and it looks REALLY clean.

Question #1: I've read about the presence of a "Q" in the vin number to confirm whether or not it has an original 428, but exactly where should the "Q" be in the string of letters and numbers? Sub-question: On the NADA classic car value website, it lists both a 345hp and a 360hp version of the 428. How can I find out which one this car has?
Question #2: If I chose to look at the car, is there any way I can pinpoint the oil leak without taking it to a mechanic?
Question #3: If I did want to invest in having a mechanic inspect the car, how much does that usually cost and should I take it somewhere that specializes in classics?
Question #4: If I fixed the windows and oil leak and the car runs good, how much would it be worth? The NADA says average condition is $16,000...
Thanks for any help!