It depends on what your plans are for the car. I'm doing a build-up of my rear as well, but I'm building it to be able to handle a Kenne Bell launching on slicks. For me, that means FRPP 3.73 gears, a trac-lok rebuild kit, motive shim and bearing kit (recommended for cars > 60,000 miles), a 31-spline carrier out of a cobra, F150, or Explorer, and 31 spline axles. If you just want the gears, and don't care about beefing up the rear, just get the ring and pinion, standard install kit, and gear oil. You may want to spring for the bearing kit, as your car's getting up there in mileage, but it's probably not necessary. As far as I know, Royal Purple has friction modifier already in it.
I would recommend doing the bearing kit when installing the gears. This will save you time later on since you already have 48k on your stang. Kill two birds with one stone