BLM's Flare Star looks like it could potentially be kind of an messy to use, as you need to use 6 Fire IVs and with a 3s cast you need to Swift/Triplecast it... I also kind of wonder why Flare Star is an AoE because it's never going to be usable in an AoE situation as you'd need to cast 6 Flares in a row to use it as an AoE spell... Unless you're using Fire IV to single target trash mobs...

And if you want to use Thunder, you need to let Astral Fire drop to become unaspected in order to gain a new Thunderhead to recast Thunder.