If you go more than 1 inch you will probably need caster/camber plates that allow you to adjust the car back into a stock setting. You can do the springs first and see if you need them and if not this may save you 200 dollars. The issue here is if you need them you basically have to redo the install as its the same work nearly for springs as it is for caster/camber plates. Just an FYI if you pay a shop to do it or not (plus cc plates look cool).
If you want performance then I would get ford racing C springs or H&R race springs. Your stock springs are about 400lbs front/200lbs rear rate and are specific springs (how stiff they are).
The ford springs will give you a 1-1.5 drop (it depends some come pre cut some you cut if you want more than an inch~) and they cost about 150 bucks. They are a specific rate spring 600lbs front 300lbs rear.
H&R race are 700+lbs front/300~ rear (not sure on rear) and cost about 250.00. They are progressive. This means the more you push the harder they push back, so you get a better ride normally and as you push the car to turn it gets stiffer. The drop is 1.5-1.75 inches.
I would only lower my car if it was at least 1.5 inches, any less and well... it doesnt look much better than stock. So you will need CC plates 80% of the time like this.
Eibach also has springs that retain a softer rate more like stock as well as stiffer ones. Heck, a bunch of factory ford springs are made by eibach lol. They are about 250.00, I think the ford c spring IS made by eibach actually.
maximum motorsports has 4 bolt CC plates that are the best out there, they cost about 180 bucks but are worth it.
Finally, that leaves us with shocks/struts. You technically do not need to replace yours unless you car has higher miles and its just a good thing to do then. They will wear out faster (the stock shocks/struts) as they will have more load on them with lowering springs. You want your shocks/struts to be valved (how fast they compress and release) to the spring so they match in rate. Its not rocket science just in the ball park~ so your stock ones are fine if you want to wait on those until later on. Your handling wont be as good and your ride might suffer some... its not the end of the world. Expect to spend at least 200 bucks on shocks/struts and the install for springs pretty much is the same for shocks/struts so if you pay someone it might be cheaper in the end to pay them for this while you do springs.
For normal driving with a 1.5 drop (mind is 2.25 lower in the front..) I dont have issues generally. I am careful of course as you have to be but 90% of the places are accessible, you learn quick where you can and cant go and you learn to go into drive ways at an angle
I have a how to install for springs, its easy read it and it might save you 300 bucks or so~
Installing Mustang Lowering Springs
ask all the questions you want so you get what you want and dont regret anything.
(if handling good is on your mind this is the first step, then comes bushing replacement and so forth)