I'm looking to create the effect of someone walking through a room full of what look like motes of dust - as you draw closer to the floating objects (through an exaggerated camera zoom), you see they are actually photographs (ideally they would also be slightly reflective).
As there will be about 200 photos, this would be a long job to do manually, positioning all the layers in 3D space within AE.
Is Particular the right tool for this job and how would I go about setting it up?
Yes you can do this. Make two compositions> in one comp is where your particles are (1st comp)>in the other comp, place all 200 photos in (2nd comp). Make sure in comp 2, the time isnt more than 1 frame long. Place comp 2 inside comp 1. Go into the particular effects settings and set the particle to custom. Another drop down should appear just below. Select your comp 2 as the particle type. Now when you animate your particles, they should all be the different pictures. You might have to mess around a little bit to figure out how to get the images to not move. Hope this helps.