Hi Ivor
Your understanding of the definition of the files is correct, but the one that always makes me chuckle is the flat dark, why? anyway.
A Light frame is your image file plus all the other junk.
The idea of the flat frame is to take an image of the optical patch and photograph all of the debris within the path,
i.e all the junk on your filters, ccd lenses, ect. so to this you need light. As carol said, this is normally taken so the well depth is half full, so check your histogram on the back of the camera, and make sure that you have not
overexposed your image, even underexposing by 2 stops should be ok.
A dark frame is an image that records all the noise present within the camera/ccd. As the camera heats up during the exposure it produces noise,
as you said this, is normally done at the same iso, and length of exposure, so these should be ok.
A bias frame is the frame that records the readout noise from the ccd/camera.
All you need are these four files to process your image,
however!!, you need to take your flats at the same time as your lights, so that any debris is in the same place optically.
If you take them at a later date, the debris will have moved and you will get strange processing problems.
If you look at this flat that has been stretched you can see the junk in the image train.

If you set your camera up next time, the junk will have moved, so any processing that takes place using the flat will affect the image.
Bias files contain only read noise.
Dark files contain read noise and exposure noise, (no illumination problems as there is no light)
flat files contain all the uneven illumination noise.
light contain all of the above plus your image
by subtracting each of the bias and dark above from your light frame, you are just left with the image and the illumination problems
by then adjusting the exposure with the flat frame, you are just left with your image.
Now by stacking your image files you reduce the ratio of signal to noise,
so the more frames you take, the better the final image, upto a point,
adding more frames past this limit will not increase the image noticeably.
then there is the subject of colours, but thats all down to you and artistic licence.

Mac