Fiery Burst Blast all day long by reserving 1 fire spell. Adds +1 CL to fire spells.
Fiery from Sandstorm. Adds +1 damage per die to fire spells.
Blistering from PHB II. Adds +2 damage per die to fire spells. And if they fail the save, -2 to attacks and skills until the beginning of your next turn.
With just Fiery Burst, you can get the flavor of a fire blasting cleric.
Are you adding Fiery and Blistering to Fiery Burst? Because Reserve Feats are Supernatural Abilities and not spells. So Fiery and Blistering cannot modify Fiery Burst.