Regarding online roms with Gateway, nothing has changed. You still need an official header from an official cart that can play online, and you need to inject that header into a .3ds rom and rename it .3dz to play online with it.
Regarding upgrading your emuNAND to 10.7 if that's something you want to do, simply get the new GW launcher and update as normal through system settings. 9.6 introduced new encryption keys again, and if you want to play new games that require 9.6+ firmware on a emuNAND lower than 9.6 you will need the cryptofixed version, so consider updating emuNAND if you want to play newer games.