First Timer...3" lift on Little $...Blocks or Leafs?

This is my first post, first XJ, first 4X4, first lift! I have a 91 stock XJ I want to get 3" of lift all the way around. I am planning on using Grand Cherokee/ F-150 coils in the front w/ 2" spacers & Rancho RS5000 shocks. What is the difference between using blocks and adding leaf spring? When adding leafs how does just adding a leaf or two give you lift beyond the thickness of the pack?

Sorry if this sounds a little ignorant, but I am a virgin to all this.

Thanks in advance for all your help!

First, if at all possible save your money to get some RE3.5 coils for the front. Contact FullsizeXJ on this forum for a good price on them and all your other RE products. I got my RE3.5 coils from him and it was great service. I say this becuase once you get your grand Cherokee coils and spaces you would have already spent at least half of what new coils cost and would be without the spacer. Don't get the Rancho RS5000, I had them and they are bad. Go with the Doetsch Tech DT3000 they are pretty good for a cheap shock and in my opinion upon having both way better than the Ranchos. For the rear assuming you are on a budget I recommend a bastard pack for the lift, basically you take leaves from another vehicle integrate them with the XJ main to get the lift. Similar to add a leaf but far superior. I highly recommend you read this thread http://www.naxja.org/forum/showthread.php?t=50083&highlight=bastard+pack there all of your questions regarding bastard packs will be answered. I was also looking for the budget lift like you at one point to replace my sagging budget boost. I went with the RE3.5 in the front, S10 leaves in the back, RE track bar, jks quicker disco's, ditched the 2" spacers but kept the 1.5" shackles, and this gave me 4" lift all around.