If you don't have a whole bunch of track experience, then I would say you're on the right track. Seat time is really the most important thing before you start throwing parts on the car. Now with that being said, you do want a decent set of tires, solid brakes with fresh fluid, change the trans/diff/engine oil, and make sure all your
suspension points (ball joints/tie rods/ect) are in good condition before you hit the track.
SN95 and new edge mustangs are pretty capable and fun cars in stock form. You're not going to set any records, but as I think you realize, you'll get faster with seat time and be able to figure out where you want to start modifying the car with that experience.
I don't have the car that's pictured above anymore, unfortunately. Before I sold that car in 2014 it was setup for AI with a full Griggs
suspension/ect. I think all I had done to the
suspension on the car in 2007/2008 was a set of Tokico HP shocks and springs, griggs racing caster
camber plates, and bump steer kit. I had a ton of other mods to the engine and chassis by that point. The car ran really well with that setup, but you are correct, it had a tendency to oversteer with the staggered setup and primarily stock
suspension. I was able to partially correct that issue with a rear sway bar change, but it really took a fully built
suspension tuned for a staggered setup to get the car where I wanted it. The car still did well though, I got first place in SCCA SM class for my region in 2008 and didn't have any trouble keeping up with most of the pack at NJMP, Summit, and Watkins that year.
I had to hammer the hell out of my wheel well and roll my fenders to fit the 315 NT01's fyi and I had to run a 1/4 spacer. They would rub a lot during hard cornering before I did all that. You also don't want to lower your car too much on the stock
suspension as you'll affect the handling characterizes of the
suspension.
If I were you, I'd do a square setup to start off with. I'd upgrade your shocks, springs, add a bumpsteer kit, and throw some caster/
camber plates on it. I ran -3.5 degrees of camber and max caster on my car with the stock
suspension, and tire wear was flat an even on the front. Then I'd look at running a decent track pad, change the brake lines out for SS, and run a higher temp brake fluid.
And then have some fun!