Talking head with ppt slides... Best Practice?

My video sequence is 1080i60 (1440x1080) and is about two hours long...
The talent is green screened speaking to 60 slides that are off camera.

My final output is going to be a combination of just the talent on the screen, just the slides on the screen, or the talent scaled down to the lower-left with the slides behind him news anchor style over his left shoulder.

I am wrestling with keyframes, trying to scale him down and then back up.. and same with the slides... so.. I am looking for ideas/best practices... I must admit, my keyframing skills are still being developed...

Should I just create 60 separate video clips (one for each slide) and position each clip accordingly or should I keep the one clip and use keyframes to scale up and down?

Regarding the slides... I have tried exporting them as TIFF files from PowerPoint and now I don't know how to properly scale them so they look good either as full screen or behind the shoulder. I want to make sure they are still readable by the viewer.

I also experimented with importing them into KeyNote and then exporting as QT file. The slides look better as a QT file but I am having trouble marking just one slide at a time and placing it in the timeline simulating a 'still'. I am now having trouble extending the duration of that freezeframe still for the length of the audio for that particular slide...

Has anyone done this before? Once I get this figured out, then I can go to town for each slide making the appropriate adjustments... but, now I just don't know which path works best...

Thanks in advance for your expertise and insight.

-Steven