when you search firefox on the play store, there’s a brave ad

if by cache you mean that your entire system is on your drive and that the hdd is for backups or games that you’re not currently playing but don’t want to reinstall, yes.

it’s not secure by design, since it’s not made to be secure, and also uses unstable versions of a lot of packages to make certain exploits work

okay but who doesn’t want a tablet with replaceable batteries

replaceable batteries as in AA batteries

why should you open it up again, instead of just charging/replacing the repalceabke batteries

but replacing the battery doesn’t mean you get to have a tablet with replaceable batteries

yes

android is very sandboxed, so anything you do in termux/userland can’t affect the android on your phone (unless you’re rooted)