If the oil level is in between the min and max levels you're fine. If you think the car will consume enough during your coast trip to fall below min level - then top up (to max level) before you leave.

I would not make the switch to synthetic oil at this point in the car's life. Keep using what you've been using. And I'd go to a change cycle that changes the oil every 6 months or 4-5 thousand miles, whichever comes first.

And since it seems like you don't put a lot of miles on it -- when you do drive it or even start it, be sure you take it out for a good 20-30 minute drive. Long enough to fully warm all fluids to operating temperature. This will drive all the condensate (water from condensation) out of the crankcase/oil and dry out the condensate in the exhaust system.
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82 242 5.0L; '10 Cayman S; '15 Honda Fit