No that is the base cast speed of the skill. But this is irrelevant, since this skill cannot be manually casted anyway.
Same as above, this is irellevant.
No, there currently is not
Each stack has its individual duration
So as a summary its about gettign as many stacks as possible in as short of a tiem as possible.
Basically all fire aura builds have some good and steady base generation, so you can run around with a few stacks and once you start attacking or activel using abilities that can generate Fire Aura stacks your Fire Aura stacks peak into some very high numbers.
Most builds that I played ran around with ~10 fire aura stacks passively and peaked into 20-25 stacks during combat.
Havenāt ran fire aura in quite awhile but it was one of my first spell blade builds. I found it didnāt really stack up to other options. Iāve since switched over to consecrated ground aura on paladin with the Judgement skill, but fire aura may be stronger than my memory now.