I don’t think that the Church is named after St. Nicholas is coincidental. Many of the type of persons/situation he is the patron saint for have appeared in so far --

Bianca tell Matilda:
“If you must pray, why does she not bid you address yourself to our great St. Nicholas? I am sure he is the saint I pray to for a husband.”

And he would be as he is the patron saint for:
Brides (Isabella)
grooms (So he missed with Conrad, no one is perfect :->)
maidens/ spinsters/ unmarried girls (Isabella/Matilda/Bianca)

Manfred also invokes St. Nicholas, when trying to persuade the knights to his side

Sir Knight,” said Manfred, warmly, “Ricardo was a valiant and upright man; he was a pious man; witness his munificent foundation of the adjoining church and two convents. He was peculiarly patronized by St. Nicholas—my grandfather was incapable—I say, sir, Don Ricardo was incapable—excuse me, your interruption has disordered me.—I venerate the memory of my grandfather.—Well! sirs, he held this estate; he held it by his good sword and by the favour of St. Nicholas—so did my father; and so, sirs, will I, come what come will.—

Perhaps he forgot that Nick is
against robberies and for lawsuits lost unjustly (The taking of Otranto by Don Ricardo – I am interpreting lawsuit very loosely, but there appears to be some sort of trickery/manipulation involved in the getting of Otranto)
against robbers; (Don Ricardo/Manfred)

And that he is for
pilgrims/ travelers (Frederic and his Knights)

And St. Nicholas is also --
against imprisonment/ for captives/ for prisoners (Theodore/Isabella)
for thieves [repentant] (So Manfred does not apply)