Easy answer: fit them all
To give the answer that you really want ("detail what each items purpose is, and going from least to all being done what is the suggested fitment order") would probably require a good sized essay. Along with that, is the different writers' opinions and tastes, along with all the different models of cars and equipment brands/settings too, so a definitive answer is probably not possible.
Here is what I did for what its worth:
1. Droplinks front and rear fitted (cheapest mod), no noticable difference to handling but didn't have them on long enough before other handling mods were added.
2. Lowering springs (Tein). Huge difference in handling and look of the car. Also, the ride of the car was compromised, but much less body roll in corners - loved it!
2a Prodrive geometry settings at the same time as lowering springs and added to the better cornering performance noted in point 2.
3. Anti-Lift kit. Again, transfomed the handling, much better front end grip and faster turn in. Also balanced out the car in fast corners - no understeer - but still lost the backend once!
4. Removed Tein springs and fitted Tein Superstreet coilovers and downgraded to "fast road" geometry settings. Can't say there has been much of a difference between this and points 2 and 2a. I went for the fast-road set up as the Prodrive settings ran down the inner tread way too quickly for my liking. If the car loses grip and slides, then it does so with all four wheels in equal measure - lots of fun!
5. Rear ARB - wating on the call from Hypertech. I was advised by Duncan NOT to fit the front ARB until I try out the rear and see how it feels. He said that installing front and rear is to bring the car too near to a track car and would compromise everyday driving. If the front end is too stiff, i.e. less body roll, the car will "skip" across our bumpy roads while cornering at speed. A slightly softer front end will allow the car to aborb this and give better front grip under the circumstances. This will be a 24mm bar on the middle setting.
My findings, noted above, are all based on track-use. I can't say I have the bottle to really push the car to the limit on the open road, because if something goes wrong, then its in a field or in a tree - not good. The track has some nice gravel traps and tyre walls to save me, plus everyone is going in the same direction, so I push with a bit more confidence.
Conclusion:
As stated in the Introduction ( ) fit the lot! If nothing else, at least you have bragging rights, ... "Oh well my car has ..."