Definitely bring a polarizer, if you're going to the Galapagos. Use it judiciously in Ecuador - it is easy to over-polarize your skies and end up with near-night indigo sky with an otherwise obviously daylit photo when you're at those high altitudes. For the night stuff, I'm always on a tripod, and generally somewhere around 15 seconds to 1 minute 30 seconds, f-stop ranging between f8 and f22. Remember with color negative film you have reciprocity to calculate, but generally it's only 1 stop extra unless your metered exposure time is over 1 minute. What I saw online about Portra 160 is that less than 10 seconds metered exposure requires NO reciprocity correction. 10-100 seconds, 1 stop, and not recommended beyond 100 seconds. Those minute and a half exposures I've done are including reciprocity compensation. Those are rare, however - most exposures are in the 15-30 second range, including reciprocity compensation.