Ahh one of my favorite Mustang topics.
Get the Southsides for sure, tons of help for traction.
Then get a set of cheap gas Monroe shocks from Discount for about $10 a shock. They are nice and loose. I had trouble with the 50/50 rears because my car is so light.
The sway bar needs to go in the front if you want optimal traction. This will greatly effect handling. After that the 70/30's should be more thsn enough for your car,
What kind of upper and lower arms do you have ?