Need help with some part #'s /sizes

[BR3W CITY]

I need to tackle my suspension, one of the only things on my truck that I personally haven't messed around with too much.

Right now in the rear I have (I think) Jeep springs and some Nitro Drop Shocks..unfortunately the part # 7506 no longer exists so I can't really cross reference them. I'm planning on ditching those and the springs, and replacing it with a set of coil-overs. How do I know how long or short to go for the best travel/function?
The rears would need to be about "15-16 at ride height, depending on how much drop the bracket has. (I've never weighed the truck, so I don't know how much is over the rear axle weight-wise) this also leaves me confused on what spring rate I need?


for the front, I've also got Nitro shocks but they are worn out and seem a bit flimsy. Mounted they are 11.5" long, so would a 9.25/13 shock work? Qa1 makes some pretty nice street rod shocks in that size.

Any help would be appreciated; no idea how to pick some of this stuff out.