[3.8] HahaMustard's Storm Brand Inquisitor - Great League Starter!

I would advise against adding in faster casting to storm brand. On paper it sounds like you would want faster casting, as it increases the frequency of times the brand hits. However, by removing any of the 5 support gems you are actually losing DPS

According to Path of Building:

Increased Critical Strikes: -10.3 % total DPS
Concentrated Effect: -23.6 % total DPS
Energy Leech: -4.1 % total DPS
Controlled Destruction: -12.2 % total DPS
Added Lightning Damage: -9.4 % total DPS

If you really wanted to slot in faster casting, I would recommend Energy Leech but then I would also recommend swapping ascendancy points away from the Pious Path route into the Instruments and Augury Route. However I'd recommend against that, as you are grabbing in my opinion inferior nodes and losing out on a lot of defense in the build.