Well, I held off replying because I'm certainly no tech expert but I hate to see a post get no response...
A couple questions to ask yourself before you start mod-ing:
How hard core do you want to go?
Is this a trail-only rig (no need to consider street manners) or a daily driver (streetability is a consideration)?
How much money (and time if you do your own work) do you have to spend?
Once you get started it can be a never ending, very expensive, sometimes frustrating but often satisfying succession of projects to get your rig to do what you want it to.
As for spring over: I have no experience, just repaeting what I've heard (and maybe have that wrong so somebody chime in and correct me). Advantages: more lift for the buck, less spring arch to achieve lift, can be done with stock springs. Disadvantages: driveline angles, axle wrap, high center of gravity.
As for lockers: (again, not speaking from experience) For streetability a selectable locker like ARB or Ox are best (can be turned on or off). For a pure trail rig the Detroit seems to be the most popular for strength and reliabily.
Hope that helps you at least a little and maybe now somebody who knows more will set me straight.