What classic mustang year should i get?
Well if you like the shoe box fenders and quarters of the 64 1/2-66 models then be my guest. My opinion is that the 67-68 looks awsome. None can compare to the 70. Hince Ford copying the 70 in the 05 model.
The only thing about buying an older model Mustang is the engines hated low octane gas. Especially the 351C they were bad for preignition. This can be worked on to fix the problem nowdays, but head work is expensive. Besides that the Cleveland stock for stock produced about the same horsepower to weight ratio as the 351W. If you have money to burn then a good "crate engine" is well worth the time, rather than monkeying around with an older design engine.
Look in the trunk pockets on each side, right behind the wheel wells on each side, that is a problem area on the mustang for rust. also if they did messy body work it might be visable from the inside of the quarter panel. Look under the car at the floor pans. It is amazing what some new carpet in the floor will hide, saving the seller lots of money fixing the floorpans.
If you are unsure about the engine, check the dipstick, most poeple don't think to top off the oil. If it is very low, I would worry about the care they give; also light brown colored oil, means they cared enough to change it before selling... The transmission oil dipstick also, even though you cannot get a good reading, you can see if the fluid is black, bad sign also, should be redish color. Brake master cylinder should be full, if not most likely leaking somewhere. Look for wet spots anywhere on, or around the engine compartment, even if it looks washed or clean. Leaks appear in short periods, faster than most people have time to wash them off. Look under the car to see any wet spots that might have accumalated in the previous days there. These things don't take away from the sellers rep, but they do give you some barganing leverage at the point of sell. Everyone is trying to make a million with a grain of sand nowdays.