What interval between photos is recommended for shooting meteors?

Cameras wouldn't offer continuous burst modes if they were harmful to the camera in any significant way. There's no more risk or stress placed upon the sensor in a series of 400 ten-second exposures than there is in a single 67 minute exposure. Your camera can handle both without any problem. Sensor heat is something we have to accept will happen when doing any kind of astrophotography (or when doing anything that requires the viewfinder to be on with a mirrorless camera).

Of course the shutter mechanism will receive the wear and tear of 400 actuations versus the wear and tear of a single actuation, but modern DSLRs are pretty good about shutter longevity even at the entry level, where one can expect to get well in excess of 100,000 "clicks" on average.

I want to create a composite with many meteors in one frame and thus plan on shooting a series of many images (probably several hundreds) with my intervalometer.

I wouldn't use an intervalometer at all. I'd use a cable release with a button that locks down. I'd then set the camera on "Continuous" shooting so that as long as the shutter button on the wireless remote is locked down the camera will continuously take one frame after the other with only the minimum gap that the camera is capable of between each frame.

How many seconds should elapse between two frames taken? Is one second (i.e. an interval of 12 seconds) fine?

If you don't have a cable release available, set your intervalometer to the shortest possible delay between shots.

• If your intervalometer allows you to set the time from the end of one shot to the beginning of the next, set it to zero, if available, or to one if zero is not available.
• If your intervalometer requires you to set the interval from the time of the beginning of one shot to the beginning of the next shot, then set the interval to one second more than the exposure time. Then TEST it ahead of time.

Especially for exposures over one second, the actual exposure time may be a power of two, rather that the designated exposure time. Many cameras expose for 16 seconds when the exposure time is set to 15 seconds and expose for 32 seconds when set to 30 seconds. This is because many shutter time values on the commonly used list are rounded from actual powers of two to easy to remember round numbers. 1/60 is really 1/64, 1/125 is really 1/128, 1/250 is really 1/256, and so on. (By the way, aperture values based on the odd powers of the square root of two are also similarly rounded. f/22 is really f/22.62741699796952... which is actually closer to f/23 than to the number that we use to represent it.)

Shooting meteors is a numbers game. It's a low return numbers game, too. You'll need to take hundreds of frames to catch a handful of meteors.

As other existing questions here point out, the optimal technique for shooting meteors is a bit different than the optimal technique for shooting other types of astronomical phenomena. In some ways, it's almost like doing flash photography when ambient light is also present. The stars and all other light sources are the ambient light. They are "on" for the entire length of the exposure. The meteor is like the "pop" from a flash. It lasts a much shorter duration that the total exposure time, particularly when one is considering the comparative time on pixels between the stars and the meteors. The stars stay in the same place (or within just a few pixels) for the entire exposure while the meteors spend very little time on any given pixels as they move across the field of view.

The longer each exposure is, the dimmer the meteor will appear relative to the stars.

To capture meteors you need to:

• Increase sensitivity (ISO) until the light gained is offset by the increase in noise. For most current full frame cameras this might be somewhere around ISO 6400. For current APS-C cameras, it's probably around ISO 3200. You can experiment using a night sky before the meteor shower to find where your particular camera's limits, combined with your post processing workflow, are.
• Increase aperture as much as possible without losing significant sharpness. For some lenses this will be wide open, for others it might mean stopping down anywhere from 1/3 stop to a full stop or more.
• Decrease the amount of time the shutter is open from the 1/500 or 1/600 rule of thumb to around 10-20 seconds.