Unless you have someone (preferably multiple someones) who is VERY competent and experienced in ocean rescues, I would definitely not recommend using a kayak as a rescue platform. As an instructor for both sea and whitewater paddling, as well as a relatively experienced guide, I would definitely stay away from paddle-operated boats in rescue situations. Only a couple of the myriad downsides to a kayak for rescue purposes like you're describing are:
They're relatively slow - you can only paddle around 5 kts at a full sprint...and that's really hard to maintain
To if you're going to be rescuing someone in the water, where will you put the victim once the paddler has reached them? in any sort of conditions, it can be hard enough just to keep yourself upright and mobile, nevermind paddling with someone sitting on your stern or hanging off your bow
As a rescuer in a kayak you can only do one thing at once, either maneuver, or perform a rescue, it's virtually impossible to do both
If you need to tow someone or something to shore, it takes a lot of time, and preferably multiple kayakers to pull something or someone any significant distance.
You mentioned easy, quick launching at night. This is definitely not something most experienced paddlers would look for especially if it's their first time at a given location, and especially if there are any sort of conditions...surf, currents, weather, etc...
In my opinion, you'd be way better off with an inflatable boat with an outboard motor. This would allow you to be very fast on the water, launch anywhere you could get a car/trailer down the beach (or carry the boat if it's small enough and you have enough people-power) They're proven in surf, whitewater, flooding, and other water-related scenarios. If they're flipped, they will still float, if one tube is punctured, they'll still float, you can have at least 2 rescuers in the boat, one to drive, one to deal with the people in the water. You'd be able to ferry supplies and materials from point A to point B, you could carry multiple victims. The boat could have lights for night operations. The list could go on and on...
If you're set on a people-powered boat, you could look into a whitewater raft, however if you've got any sort of wind you'd be pretty well screwed in terms of your maneuverability. You'd also need at least a couple people to paddle it...
Just my 2 cents. I hope it helps...
Cheers,
West