The minimum transaction fee is 0BTC.
This transaction just takes longer (from a few hours to a few days).
Is there a risk that it never arrives? Could I respend it if it doesn't arrive?
No, it just takes some tiem

Is the transaction time possible to predict based on the transaction fee? And is it possible that a transaction with a fee of 0 BTC gets handled right away if there is a low number of transactions in the network?