If you heard a modern digital camera could only reach as high as ISO 1600 or 3200, you might think it was a very limited device. Such is the case with film, though. That does not mean you can't shoot it a night, though; in fact, it can be quite rewarding, especially if you enjoy long exposures. This great video tutorial discusses shooting film at night (particularly long exposures) and how to go about it to come home with the best images possible.
Coming to you from Willem Verbeeck, this awesome video tutorial discusses how to shoot film photos at night. While there are some similarities to shooting low-light long exposures with a digital camera, there are some crucial differences you need to be aware of, perhaps the most important being the Schwarzschild effect, commonly known as reciprocity failure. This is the term for the fact that film has a non-linear response to low light; in other words, at certain level of darkness, the standard relationship we are used to (exposure being equal to intensity multiplied by time) breaks down due to the film's properties. This means you will need to be ready to compensate with longer exposures than you might expect in certain situations. If you are dealing with a temperamental stock, you will want to pay particular attention to this. Check out the video above for the full rundown from Verbeeck.
All great points. Reciprocity Failure compensation varies greatly from film to film, and you might have just given the curve for Portra 400. One thing about e6 films you didn't mention is white it's true they are more unforgiving in terms of exposure, but many of them have better reciprocity characteristics (like no compensation needed out to a minute or more). One thing that makes night exposures (and well, any time of day, really) is a spot meter, where you can accurately meter the parts of the scene that are important to you and make a weighted mental average between highlights and shadows.