Good start.
(Being on Fat 32) You dont install the nsp. You just go with the .nro as in older RetroNX installs.
But you actually have to (backup saves and) delete the older files from the RetroNX install, otherwise you'll end up with a black screen on launch. (There are config files in folders that dont match with the newer Retroarch versions > blackscreen)
And all of that is mentioned in the release blog posting. Btw.
I dont think, that you are able to install nsp without using a CFW, which would require you to use RCM mode (a dongle, a jig, ....).
Also - maybe dont install Retroarch as an nsp on 3.0.0, while there is no reason to do so?
Once full speed N64 cores have released - different story. You can then nag folk with "which version should I use, should I update (without burning fuses), should I.." but I am not the guy to ask those questions currently. (Havent updated to use pirated games like most people.)
--------------------- MERGED ---------------------------
*Snicker* You are not.