The whole point is to not go online with CFW/homebrew. As long as you don't do that, you don't get banned. Also, emuMMC & sysMMC are separate so they don't share anything except the hardware they are on. This means your progress in games otherwise known as save files are different for emuMMC and sysMMC; they aren't shared between the two.
The latest update always includes data from previous updates. I don't recommend using DZ, which is the real name of the app that you're referring to. I highly recommend switching to
TinWoo Installer instead. Its what I personally use.
I've never heard of a decryptor myself so I advise staying away from those. Title keys on the other hand are more useful for decrpyting games on your computer. When you install an .NSP file of a game, the title key is embedded within it such that the Switch uses the title key to decrypt the game so you can play it. This means you never see the title key because you don't need to.