You will probably need to do at least some of the side quests before the main quests. You can delay the main quests as much as you wish, despite a couple characters claiming certain things are urgent, and usually it is best to do them last.
Like Born2beagator said, in general it is better to mindread first, then clear opponents, then turn in quests. However, it isn't necessary to obtain the maximum possible experience in order to survive. If you start having trouble with the only available areas for combat, then it wouldn't hurt to turn in a few side quests. If you have a bunch of quests open and just want to clear some out, go ahead.
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