Portra 160 is an amazing film, especially for mixed lighting conditions where you have a blend of tungsten, fluorescent and "daylight" balanced light sources. Quite honestly, with that film specifically and with color negative film in general, you really don't need to worry about color correcting filters. If you want to see some examples of what it can do, take a look at my San Francisco nighttime shots -
About the only filters I'd be worrying about at that altitude would be the UV and maybe a polarizer. Where are you going on the trip?
Your best metering strategy if you have a spot meter, is to pick an object that you want to render the brightness equivalent of medium gray and set your exposure accordingly. Color negative film has so much latitude that you don't need to worry too much about controlling contrast. If you are not confident in your spot metering skills, then stick to incident reading as a general practice.