realistically, an XV level 1 front and rear setup (optimized factory setup) with some 17-18" rims and good tires (say, a BFG KDW, michelin pilot sport, or Bridestone potenza RE050) will be more than enough suspension for 99% of the drivers out there and should pull ~1G or a little more on a skidpad.

you're looking at $2300+ rebuild parts, and maybe some tubular A arms (if you need/want more caster) for front and rear suspension....

of course, with an alterKtion you get rack and pinion steering, better header clearance (which doesn't buy you much without custom headers anyway), and potentially cheaper big brake upgrades.

if it were me, if you're just looking for crisp, modern street handling/feel, I'd seriously look into the XV level 1, some 17" rims with 235/55R17's or 255/50R17's (or 18" with 235/50, or 255/45R18) and a firm feel stage 3 steering box.

if you're looking to upgrade the brakes, I'd go for Dr. Diff's 13" front and 12" rear kits that utilize a lot of stock late model mustang components (calipers, etc), so replacement parts are easy to find.