Fleurons means here the ornament in form of flower located on a crown, like a laurel wreath.

De foi trempée is a poetical inversion. Standard French would be trempée dans la foi, i.e. steeped in faith.

…épopée des plus brillants exploits is more a superlative than a comparative. The deeds are not compared to anything particular. That just means something like “…an epic made of the brightest achievements”.

You might also have trouble with ceint which is a very rare verb in modern French (ceindre), meaning encircled. Derived words like ceinture (belt) are common though.

Finally, the word valeur has a meaning mostly forgotten in modern French: ta bravoure, ton courage, i.e. your bravery/valor (not value.)

You found jewels and flagships because fleurons is often used metaphorically to designate the most precious item of a collection (of jewels) or the best ship in a navy fleet.
De foi trempée could refer to the phrase “une épée à l’acier bien trempé”, i.e. a strong blade: their soul was plunged into faith like red-hot steel is plunged into water to cool it.