Plan on it taking an entire weekend if your doing it all at once. I probably had about 4 hrs in redoing the back seat and another 4 in the fronts. That doesnt include removing them from the car. I also used the opportunity to completely clean the rest of the interior while the seats were out.
http://www.tmiproducts.com/mustang/
If you havent looked there they have very good installation instructions for there products along with videos on you tube so you can see what all is involved. You can always buy the kit and have a uphlostery shop install it if you think its to involved for you. Its not to bad you just need to take your time and have paticence.
I dont know why they dont include front foams with the kits, since they say they are required I think they should to but I guess they leave that option up to you. I know on 96-98 cars the seat cover is glued to the foam and thats why you need them for those. You will also need them if you want to go to a cobra/mach style seat from a V6/GT since the bolsters are different.