1. No, this does not close the forum. That option was removed as it was unreliable (on re-opening).
2. Database size and backup size are completely different things. Gzip will reduce the size greatly.
3. You do not normally need to use those options, in fact, if you did repairs daily it could possibly be detremental.
4. There is no reason not to use them if you prefer it - on most systems it will make very little difference.
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