Not judging but just fyi, that's like the worst of both worlds tbh. The point of installing independently of the base system is that the system is immutable and easy to roll back to a previous state, if you use a mutable system and also install packages with other means, you're working around a limitation that isn't even there and wasting more space to get almost none of the benefits (aside from easier permission control for Flatpaks)
Proton explicitly enabled keeping 2 free accounts on the mobile apps quite some time ago, probably more than a year, so they're cool with you having 2 like that.
If you get more, you'll be hampered at the application level, but, unless it's like a load of accounts for spam purposes, having just a handful shouldn't get you banned, I believe
Selling is outside the scope of the licence, you can do whatever you want with monetisation, be it free or paid-for.
But any one person that uses your GPL if local, AGPL if local or through a remote service, has the right to request you a copy of the code and you have an obligation to comply and provide it
Not judging but just fyi, that's like the worst of both worlds tbh. The point of installing independently of the base system is that the system is immutable and easy to roll back to a previous state, if you use a mutable system and also install packages with other means, you're working around a limitation that isn't even there and wasting more space to get almost none of the benefits (aside from easier permission control for Flatpaks)