I would hold off on the mid-pipe. Don't try to spare any money on the converter. You will just regret it later on. I would look into a precision industries stallion converter. Many guys on here have nothing but good things to say about them. It's what I'm getting when I get the cash. Check them out at Precision Industries.
Then get your gears installed. Any left over money I would do a tuneup. JMHO.
I would go with 4.10 for an auto, then a good converter don't go cheap on this like mentioned already you will regret it. TB a fms 65mm would be good and a 73/76 maf should work fine. try and find a used intake to macth the heads you get to really wake her up.
Oh yeah, don't forget the tranny cooler also. This is a must when adding an aftermarket converter. They give off a lot of heat, so you will NEED to have one on there when you get the converter installed.
first thing i would do when u get your car is do a tune up and an oil change, you dont know how long it has been since the previous owner did one.
Then as far as mods go i would start with gear (4.10s) for an auto, then either get an intake manifold or start your exhaust, since you have the cash you can do full exhaust. I wouldnt waste ur money on a TB or MAF until you have a intake manifold.
4.10's with a supercharger is too much, especially for an auto, i'd do maybe 3.73's since ur an auto, i know 3:55's and a supercharger is a good combo for 5 speeds