Mustangs Plus Grab a Trak suspension questions/Overall suspension Q's

I did a search and found a few posts about this Mustangs Plus Grab a Trak suspension upgrade. Its seems pretty good for the price and seemed to have pretty favorable reviews on the forum. I had a few extra questions though before I order a suspension kit...

Link to the suspension kit

How does this kit compare with the more expensive NPD Street bandit kit? The street bandit kit is more expensive, as I would have to purchase the leaf springs/hardware separately.

I can add upper and lower control arms to the grab a trak suspension kit, but I dont know if I need them. How can I tell if they are necessary to replace? I know they were replaced back in 1997, the car was driven daily until 1999 or so, and then sat in a garage and driven infrequently until about a month ago, so there cant be a ton of miles on them.

For the rear springs, I can upgrade to a 4.5 leaf spring in the kit. Should I? I read that 5 is a bit too stiff, but 4.5 would be good. Will this hike the rear end up any? The kit states it will sit at stock height in the rear with a 1" drop in the front.

Just FYI, i'm currently trying to contact Opentracker for suggestions/pricing as well... Car will only be street driven with no track use...