Question regarding traps

Since I have never made a trapper before, I decided to start Delve with a fire trap build. I have a few questions about traps and their support gems.

What is the primary difference between cluster traps and multiple traps? I read in the description for each that cluster traps tosses a "set" of traps clustered around an area while multiple traps throws several in a straight line. I have been using multiple traps so far, but does cluster traps offer any advantage over multiple traps?

The new flamethrower and lightning spire traps seem interesting. I know fire damage can ignite while lightning damage can shock. Based on the placement of the shadow in the skill tree, lightning seems the more accessible element since there are more lightning nodes in his area; however, ignite can be boosted by his damage over time passives. Any thoughts on one versus the other?

As for auras, I am in a quandary about anger versus herald of ash. The herald reserves less mana, but anger adds that flat fire damage. Similarly, if I choose ultimately to go lightning, the same dilemma applies to wrath versus herald of thunder. I can't decide!

I should say I play solo self-found, so I will be limited to what I can find. I know I will never reach the ludicrous damage other trappers have attained, but I wanted to try a different sort of character.

Thank you for any help you can give!