No to 1,2,4. Look for a “powers not at war” box in the rules.
For 3, you can move to any sea zone which is not adjacent to Japanese territory. So you can totally move toward Japan, eg to SZ16 or SZ17. Just remember that if you move to SZ54, you can’t use the naval base there until you are at war with someone.
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The rule that you quoted deals with airbases that border more than one sea zone, not sea zones that border more than one airbase. The point of it is that an airbase in a territory that borders more than one sea zone may still only scramble three planes, not three planes into each sea zone that it borders.