- If I were to use 2 way crossfire (two of the same GPU) does that mean I can now use 6 screens (three on each card)?
No. The only way to use the additional 3 video outputs on the other card would be to run it without crossfiring it. You can run multiple GPUs in a computer without needing to crossfire them.
- If I can only use 3 screens, would I plug the screens into the graphics card closer to the CPU or further from the CPU?
It doesn't matter. AFAIK, crossfire and SLI are smart enough to recognize which card is intended as the master - that is, whichever has the video outs attached.
- Do I need a crossfire bridge for the graphics cards?
Not for modern GPUs on modern motherboards which are crossfire certified. It may also work in other circumstances that are less well-defined, but your GPU and motherboard should not require a crossfire bridge.
I feel like noting that your CPU has its own GPU, and your motherboard has 3 or four video outs of its own. If all you are trying to do is run more than three screens, not all of which will be used for gaming, then you could run up to three screens off of this integrated GPU if you enabled it in BIOS. You would need to install Intel graphics alongside AMD's, but that should present no problem. This way, you could support up to six monitors without needing to add a second GPU.
Additionally, you could add another small GPU with three video outs - like an R7 240 or GT 730 - which could be used alongside your other GPU systems to provide a further 3 screens - up to nine.
NOTE: As it currently stands, your GPUs will all need to use a displayport connection for connecting a third monitor. This is something that needs to have an active adapter dongle attached to it if you will be using it to push a signal to a screen which does not support displayport (e.g. it uses VGA, DVI, or HDMI inputs exclusively).