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