I have read, just about everywhere, that Steeda ball joints require a bump steer kit. Wouldn't that throw the tie rod and control arm out of alignment of each other? I don't know exactly which tie rods are there but about a year ago I had them replaced and when I installed new struts I noticed they were Moog, and they also have a nipple for grease. Is that what your talking about? Or is there a specific kind? I do have CC plates, and they asked me if I wanted anything special with the alignment but I just told them to align it within spec. Nothing special.
When I replaced my struts I also replaced the spring isolators and noticed Sportline stamped on the springs. For the longest time I thought they were Pro.
Recommended but not required. You'll only want a bump steer kit if you get, bump steer (they should have called it an anti-bump steer kit in my opinion).
And yes, sounds like you already have tie rod ends with grease fittings, so you're good there.
Those Sportlines are most likely the root of your handling issue. They lower the car too much as it brings down the roll center below the car. That's probably why your front control arms and tie rods are at that steep angle. I bet the stance looks good though. Unfortunately, stance and handling do not really go hand in hand.
Now that we have all the information, my recommendation is to swap out those Sportlines for H&R Race Springs if you're not going coil overs. They don't lower too much and have a spring rate that your Bilsteins will handle, which makes for a nice riding and better handling Mustang.
Since you have CC plates, you can get a better alignment than stock. I hope those CC plates are Maximum Motorsports' as they give back an inch of travel after lowering so you're not bottoming out the strut.
Regardless, max out the caster. Set camber between -1 and -1.5. Zero out the toe or 0.15 toe-in.
I have mine set to 5 degrees caster, -1.5 camber, and 0.15 toe-in for street driving and when I do open track, I add more negative camber (approximately -2.5 or -3 degrees, which also causes the the tires to toe-out which is what you want on track). I mark the CC plates after the alignment shop sets the street setting, so I can set it back when I'm done with the track event.
Hope that helps! Corner ponies FTW.