Arrant Pyromancer was my first character back then.
From what I remember, BT only ever hits once. Doesn't matter how you cast it. So no reason not go for full circles most of the time. Probably the best CA for farming in the game. Just run into a horde, kite for a while, then send a Tempest behind you to kill everything with the fire DoT.
Fireball was great for single targets and enemies that tend to move a lot. Packs a punch and the homing makes it very usable. With 2 Area of Effect damage dealing, homing fireballs, it can easily work as your main CA. Not to mention it's basically your only option when terrain is not in your favor for BT. Similarly, I found the Frost Flare for Ice Elf very useful too, be it the massive slow or stacking DoTs.
Incendiary Shower is the boss killer of course, able to perma-stun bosses. I only used it against tough/large enemies/bosses,but it's damn good at what it does. Personally found it much safer to use than Glacial Thorns, which requires the enemy to be still and can be very problematic to cast correctly, especially against large bosses like the dragons.
Combat Art range is good, but absolutely not necessary on a fire Elf, even potentially counterproductive with the Shower. Much more useful on the Ice and Arcania elves.