What's the best way to protect my rooted Android 7 from malware and hacking?

Considering I have to use cellular data and being ***not*** connected to the internet is not an option, what measures can I take or tools I can use to keep myself protected from prying eyes? My first step will be to do a clean rom flash in case I'm infected already, but as soon as I do that, I'd like to ensure that I remain clean and protected because I would be using my phone for very private data. What can I do? Besides the obvious and common sense stuff of course. Android 7 | Rooted | Moto C Plus