I don't know what you meant by πρὶν ἀπὸ. I know that πρίν is usually followed by a temporal clause
rather than being used in this manner, as a preposition, though I may be wrong.
and ἀπό needs gen. but doesn't have the meaning of above.
There isn't πίστη, but there's πιστή, though it's the adj., meaning loyal, trustworthy (female).
ὅλον is the neut. form.
I remember in Plato, and according to LSJ it's common in Herodotus and Attic Prose
περὶ πλείστου means above all, to denote value, which seems to be your intended meaning.
now all that's left is to find the right word for loyalty.
EDIT: ἡ πίστις, can mean loyalty.
also τὰ ἄλλα, neut. pl. substantive of ἄλλος, means all else.
so maybe πίστις περὶ πλείστου or πίστις περὶ τῶν ἄλλων.
[changed to neuter. gen. pl. in the 2nd option. sorry for not catching it sooner.]