I just know I have to change springs at least, before I can get a warm fuzzy for the dampening.
That's not really 100% correct. The springs are important, sure, but it sort of strikes me that you are operating in the dark here to some degree.
Here is how you should approach this:
1. set the compression and damping in the mid range. Check to see the rebound of the suspension (by compressing and releasing) and get a feel for how the bike reacts (either by riding and/or by pushing the springs down and releasing).
2. Once you have done that and have the compression and rebound in the ball park. Then measure the static sag, free sag and rider sag (with the preload completely off).
At that point, you can figure out what you need. Even with incorrect springs, you should be able to setup the suspension so it will operate pretty nicely. It might be a bit stiff and your sag settings might be a bit out of whack, but I think you should try to dial in the current suspension first, before you start making a lot of changes. That will teach you a lot in the process and help you understand what you are trying to accomplish here.
Again, having the correct springs for your weight and the bike's weight is a great idea, but you are remiss to completely skip the compression and rebound settings at this stage - in order to see what you are working with and learn about where things stand currently.
Also, keep in mind, OEM suspension is a compromise. Even with better springs and valving, it will never be as good as true after market suspension. Valving will help and so will springs, but for what you are dealing with (i.e. swapping suspension between bikes), I think you should step back and learn a lot more before you start making modifications.
BTW, I have a video up on youtube (where I change springs on my Ohlins forks). You might enjoy watching it if you are about to tear into your forks. It has some helpful tips and will give you an idea of what you are in for! :-)
As always, if you have any specific questions, just fire away. Sounds like you are on a fun project for sure