You can use the stock struts and shocks, but they will wear more quickly with the car lowered. What you will need is caster camber plates. I, along with many others, recommend Maximum Motorsports 4 bolt style. I've had them on all 3 of my Mustangs. You don't want to compromise with suspension.
Without the upgraded shocks and struts, you may find your ride a little bouncy. Especially with the stiffer H&R springs. In my opinion, shocks and struts just complete the whole package and provide a nice setup along with some adjustability (depending on what model you get).