There are so many ways you could setup the S800. I have used it as a single man setup with the up/down axis on my controller but lately I have really been enjoying the benefits of having a dedicated camera operator. I did not run into any problems when I would FPV it through the gimbal but I probably have more FPV experience than most people and learning to do it on a rig like the S800 is probably not the best idea! This post will focus on the 2 man setup.
Here you will notice that my IMU is mounted on the retract servo. I was about to throw my S800 away because it would blink white lights and start losing altitude. It was frustrating and I tried EVERYTHING! I bought Secraft arm strengtheners, balanced the props, took it all apart etc etc.. nothing worked until I finally moved the IMU to the vibration dampened landing gear. I am now in love with my S800 again!
For my remote control, I use the Futaba T8FG radio. It feels bullet proof and I would recommend it to anyone. It also has S.Bus which really makes working with a multicopter easy. The second controller is an extra one I had laying around so I hooked it up as the gimbal control. The gimbal control handles the direction of the gimbal while I maintain "control" of the Zenmuse (I can center the gimbal, take control, etc) and the shutter on the Futaba. In order to get this to work the way I wanted it too, I had to get a satellite RX to take advantage of the extra channels beyond 7/8 that the Futaba RX offers.
For my video downlink, I use the immersion 5.8ghz from ReadyMadeRc.com. These sell out frequently, but do yourself a favor and just wait to get one - they work the best and I wouldn't trust my rig to anything else.
My ground station is very basic and portable. That also means that my range is usually limited, but I don't ever fly out of line of sight anyway so it doesn't really matter. My current favorite FPV goggles are the Fat Shark Dominators because they have a crisp image and a built in 5.8ghz RX to keep the wire tangle to a minimum. The built quality is still terrible, but there really is not another option yet. I use electrical tape to try and secure the eye cups and the battery.
When I need for someone to direct me or give some guidance on how they want something shot, I hand them my portable monitor which has a built in 5.8ghz RX. It is really only useful when the S800 is close by because its antenna is not very good.
The EOS Sentry battery monitor is an absolutely essential tool to carry around. I have four batteries and even though I have them all marked, it is still to panic before you fly if you can't remember charging them. If you fly an S800, buy this and check your batteries before you fly - Simple!