“Is binn an tost”, or “bíonn an tost binn”, I think would both be acceptable. There is a slight difference in meaning. The first means that silence is inherently sweet, the second one suggests a habitual thing – that silence is sweet every time it happens.
The second one is going to be more problematic and highly variable. The word “soul” doesn’t translate well here, as the meaning of “living thing” doesn’t really apply in Irish. “Ná cuir do mhuinín i nduine ar bith” = don’t trust anyone, alternatively “ná biodh muinín agat as duine ar bith” is another of the many ways of saying this.