pure str sword is correctable, just buy a blade

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But to your question.
Quests can be done later, and they lvl you faster. If u want to seriously sp farm, dont do quests till u have reached your gold.
Fire has the most damage.
Ice has less damage, but freezes people. Better at lower lvls, but weaker at higher lvls.
Lighting i personally think is the weakest overall, but various people disagree with me.
Remeber, its all your choice, and why not have 2 force trees?
And no need to dev force, just pot it up. More effective, and faster.