Still trying to find my way since purchasing N4 in the sale.

Initially installed the official libraries to a non system drive but then started having problems with libraries and skins not showing up so I deleted them and downloaded a couple to my system drive, however I'm not sure this was the problem after all?
Anyone have any experience of alternative drives for the libraries on OSX?

Thanks to other members here I came to realise that my N4 licence also gives me a version of N3, so I installed that too and have been having a look there.

Apart from the official dlibraries, I've downloaded a few of the third party libraries from here but am having issues - prior to installing N3 I couldn't get Surge EQ to load in N4 - is this an only N3 library as it loads great in N3?
What is the difference between N4 and N3 libraries?
How do I know if one will work in N4?
How do I know where to install - iunto the N4 or N3 liobrary folders?
What is the difference between N4 and N3 skins?

Would getting hold of a copy of NAT help for my N3 fiddlings - if so where can I get it?

Many thanks all!