I am not sure what the compression difference is between DV and BetaSP, but over all PRemiere Pro’s keyer is less than adequate. Would you happen to have After Effects?
There are no “best settings” The settings depend on the duration and the quality of the video. In this case, since your video is only 10 minutes in length, I would do a 2 pass VBR encode along with the maximum bit-rate.
If you already have your image slideshow on the sequence, create another sequence and via the Rate Strech tool, simply adjust the duration as required. If your current per-still duration is 5 seconds and you have 20 stills, simply increase the duration by 40 secs.
Set up yout stills in a bin and use the ‘Automate to Sequence’ option from the project window. This will place the stills on the timeline with the Cross Dissolve transition between each of the images.