might/would - always belongs in the main clause. Which book are you learning from?

Yes, if I understand your question. The word "might" indicates possible action. The word "would" can indicate habitual past action. "As a child, I would play in the woods every day". "Are you going to the movies tonight?" "I might go. What's playing?"

I've seen a few language forums and blogs where the matter is discussed (eg. "If I would.... then I..."). As much as it could be argued as possible (both are technically past tenses of will/may), the general advice is DON'T ever do it. You would then need to defend your reasoning for doing so, and even then your justification may not be considered acceptable. It's better to write a clear sentence for your reader than expect a technicality to do your reasoning for you.