Hi Russell,
The Sony A7s has a good reputation for low light, low noise imaging.
You would need to test it out on the star in question, with your chosen scope, to see how it would go as a movie mode device. That would be an easy first step, and something you would do anyway to get a good experience with the field of view and the behaviour of your camera.
Traditional occultation recordings have precise timekeeping as a major input to the science. As Jonathan says (above) the central flash is the big money for the science crew, but good timekeeping will still be very important. For example, if you are close to (but not right on) the central line, your central flash recording will display a different behaviour to a dead centre line. Now if the field of observers is densely packed and we get a lot of chords, then yes we may be able to retrofit your chord to the rest of the pack based on your location. This is not ideal, but desperate people can do desperate things :-). Also bear in mind that Pluto has an atmosphere, and the soggy ingress and egress light curves do nothing to make that retrofit alignment task easier.
If the field is not packed and we have few chords, then timekeeping, preferably to the millisecond and referred to UTC, is really quite necessary. At the very least, syncing the camera with the computer clock will get you to within a second if the computer is running Network Time Protocol and it is properly peered to a local server. But be aware that NTP has to be running, and working, and for that something like Dimension4 or TARDIS, and a good ADSL link, might be helpful.
Most of the regular occ people who correspond here use GPS based video time insertion of one flavour or another, and analog video cameras.
I am currently reading Bruno Sicardy's paper on the central flash of an occ of Neptune in 1998:-
http://www.lesia.obspm.fr/perso/brun...s_icarus98.pdf
which is a bit to get through but I am getting to appreciate the science behind the observing of the central flash, and in particular what observers (such as us) might want to do to prepare properly for the event.
Again, I would encourage you to observe the Pluto event. It is probably a once-in-a-decade occultation for brightness, and a once-in-a-lifetime chance to help out with a NASA space probe data collection.
Regards,
Tony Barry
WSAAG