Installing those won't change the fact that you'll still be on 9.2.0. If anything you're making a franken-firmware and the -20 will be changed to -30, but as far as it's concerned you'll still be able to do anything you could've done normally on 9.2.0 + eShop and NNID stuff.
And yes, you can install them on sysNAND. You should be careful however as if anything goes wrong you could brick the system, but I've got those .cias installed on my sysNAND and haven't encountered such problems yet.
Actually they need the latest TIGER as well since HANS eShop spoofer no longer works with just NVER alone; the entire menu just freezes. I'm using the latest TIGER myself and using your FMP app + booting into sysNAND I'm able to run it on the home menu in 9.2.0. If anything I've tried using HANS afterwards and it doesn't work as far as I'm aware, so FMP + TIGER + NVER is the way to go.
And strictly speaking for the purposes of what the member wishes to do, no they don't need to install mint but assuming that for whatever reason they wish to add funds or go purchasing anything, they will need mint so it's best to just add that in as well.