...
If you are going to capture 2 or 3 performers at the same time, 8 or more cameras will most likely be needed, especially if actions are in very close proximity to each other, 6 cams will do ok if actions are not very close in most cases.
(Remember each performer needs to wear different colors)
A head mounted Move works better for slower actions where the performers head doesn't move much, slower and more consistently moving. (jumps, bounces, rolls may not work as well)
It doesn't work as well for fast actions, like fighting, or dancing, as unless it is very stable mounted on the head, it can bounce, or move without notice and throw off the whole recording, as the data is captured during the recording, and if this changes a lot during performance, it will show in the tracking also and cause more clean up, or possibly a complete loss of usable tracking unless manually edit the head in post, not fun.
If you don't use a Move on the head, you should keep any performers hair, high collars, or anything from blocking the back of the neck, this will greatly help in the tracking process with PS Eyes, or the neck bone can and probably will not follow the video well at all and cause issues.
It basically takes 3 cameras minimum always being able to see all body parts for better results in tracking, but the tracking view port only uses one camera at a time to track, so it is possible and you may have to switch the cam view at times if you loose tracking, but then always try to switch to a main tracking camera, a head on camera works best, it doesn't matter what camera number it is.
Also only one camera can detect and use the colors, (so if you switch cams during tracking you may need to re-evaluate the actor colors if getting bad tracking and re-evaluate again when switch back to main cam), this would be based solely on your particular light set up, why it is best to have consistent ambient lighting set up, doesn't need to be overly bright, just adequate and equalized around the performer(s) and direct overhead lights should be avoided, it may look fine on the video itself, but they will wash out the colors once in the Studio tracking.
Each camera you add will impact the tracking fps speed by approx, .3 with a higher end graphics card, possibly more on lower end cards, I have a GTX 970 FTW and each cam adds .3 to the processing speed as a comparison, just something to be aware of.
If you are into modification of a Move to be lighter for head use, I show a post for the gloves I made and the same process can be used to attach to a headband.
Post is here:
viewtopic.php?f=2&t=9665You are going to have additional clean-up anyway in post, but the tracking should be fairly consistent throughout the capture if done with consistency each session.
Good Luck with your projects!