Apart pen and paper you cannot trust anything you didn't build yourself from scratch.
And then you have no clue about the vulnerabilities of your creation.
At one point you have to balance paranoia vs practicality.
I think you need 2 systems : one that is connected and where you control carefully the data that it might leak about you and a non connected one, heavily encrypted where you have private data.
no wifi card, Ethernet port glued etc
