Elements are chosen to adequately deal with most factions. Change to appropriate counter-elements if necessary.
Heat synergizes with Cascadia Flare but an Electricity focused build should obviously use another Arcane. Conjunction Voltage is fairly weak so other options like Secondary Outburst (if you're willing to play into the combo stacking playstyle) or Secondary Merciless if you're lazy.
Secondary Shiver sounds like a decent option on this build because of the spore gimmick but they aren't a quick and reliable source of Cold procs on enemies so many times it gets beaten by other arcanes.