USMRacing, Seth Johansen (I think that was his last name) got the distribution for Ironman in the US, however I believe he has since dropped it. Not sure on the reasons and I am not sure if they are selling direct now or not. I would check on after sales service when you buy these. Can you get a shock warrantee'ed if you need to?
As for doing it in steps, yes you can, however you will be doing double work, but if you are not paying for labor, then it is ok. The stock shocks will limit your travel, and the ride won't be as good as it could be.
Caster:
We install caster kits in all the lifts we install. There is just no reason for not having the truck handle as good as it should. People that have not installed the bushings normally do not have the tools, so they justify that the truck drives ok. We have done the bushings in a couple of truck where the owners could not do it and drove it for a while without and thought it was ok. In every single case, they remarked on how much better it drives.
J Springs
One thing to keep in mind is that the OME stuff is not sold as a lift kit, neither does OME market it as such. (that is for the 80.) It is a replacement suspension that can handle more weight. The fact that the truck is lifted with the suspension is just a function of spring rate and extra weight carrying capability.
It is only in the US that we are obsessed with inches, so people want to put a number on the total lift that one gets. Also, the suspension is designed to carry extra weight in the back of the truck, so typically the truck has a raked stance. For some reason people don't like that and then the lift the front more to compensate. The problem with that is that when you load the truck, the rear will go down and the truck will sit like a 4Runner with it's back low.
Also, a lot of people don't match the spring selection to what is on the truck. This way, they get a higher lift but a bad ride. It is very important to match the load to springs.
The other effect of going higher in the front is that you loose caster, thus driveability. So when you plan your suspension, make sure you don't mess that up. Also, if you can drive a truck that has the same setup as you plan to do and see if you like it.