Frank,
I hope you don't think I'm raining on your parade here but I think you are being very ambitious to even consider that sort of focal length with your setup. You mentioned in your initial post (3 arc min error) to get nice tight stars you would need to get the error within 2 arc seconds. i.e. 90 times more accurate than that. To image at those sort of focal lengths for anything more than a couple of short seconds, you need to autoguide. Obviously not possible with the astrotrac.
I mean give it a go, but ask yourself why people spend so much on expensive equatorial mounts and autoguiding setups etc.
As for exposure times etc, well I fear your exposure time will be limited by what you can get away with without the trailing becoming objectionable.
BTW Ron Wodaski's program is here;
www.newastro.com/book_new/camera_app.php
Frank the purpose of flats is to remove irregularities like dust motes, vignitting etc. You can take stock flats as long as your camera doesn;t accumulate too much extra dust. Also you must take flats at the exact focus you shoot at.
Darks are, well I think you know what darks are. Of course you MUST shoot darks at the same temperature but you can build a library of darks.
Bias frames only need to be taken once using the shortest exposure your camera will allow, with the lens cap on). The purpose of bias frames is to remove an uneven brightness caused by the cameras electronics as it reads the image off the chip.
  