well the good news is that there is not a huge amount of difference between 5 and 7. The general workings are the same. Going from 4 to 5 there was a huge leap forward in the technology. 6 and 7 improve on these features but add very few 100% new features.

the main things that the average user see is that there are new types of lights and improved render features and mt6 files (material files that store all the information for a figure like a mat pose file).

Ya can get confusing what goes to who.

I only have one runtime (internal) and it is 40 gig, yet I can quickly find what I am looking for.

This is because of how I organize it, this is the method that works for me, but perhaps something like it would work for you. Even feel free to do it exactly like this

inside my "Character" folder i have folders called "Guys" "Gals" "Hair" "Vehicles" etc, then inside the "Gals" Folder I have folders called "A3" SP3" "The Girl" "Vicky" "Kids" then inside the Vicky folder I have it divided into V2 V3 and V4 so if i am looking for a item for V4 I just go to Gals-Vicky-V4 and I know everything in that folder is for V4 (I also break the folder down into free and market and then by merchant so I know what is is if it is free who it is for and who made it ... but I am pretty anal retentive)