1. Focus. Go with manual and set at .3 meters?
Be very careful with that approach otherwise you might come back with a whole trip of not-quite-in-focus footage when you look at it on the big screen. I don't know the exact optical physics of your port but if it behaves anything like the ports I have owned then I would go auto most of the time and keep your lenses and ports absolutely spotless so the camera doesn't focus on dust or scratches on them. But if you are shooting pelagics and it's a bit murky then "momentary auto focus" on something about as far away as the pelagics are, or on your fin or your buddy. The camera will then stay on manual focus. I like to do this regularly and not just leave it. If you go auto then check the footage after for focus hunting on the biggest screen possible (or on your viewfinder if you don't have access to anything bigger). I have shot stuff on 0.3m or whatever the camera gave me on a manual focus and then left the setting on and noticed later that footage is not quite sharp, particularly close-up footage. That's why I prefer auto if I'm fairly confident it won't hunt. If you're shooting macro then you have more time to switch between auto and manual depending what you want to focus on.
2. If I recall people were split on filter or no filter? If shooting up to the sun to get the big school shot do you use the filter and WB or is the shot going to have to much red in it?
I would mostly use the filter. Experiment with white balancing on the sun, your hand, and something white. Too much red is easy to take out in post but blown out green/white is a problem. Watch carefully for ND prompts from your camera and act on them! Remember the red filter is taking out a bit of light as well, which is usually a good thing for these shots.
3. Confirming most felt that it was best to WB around 30ft? That any deeper and the camera has problems?
Depends on how much light there is and how dirty or green the water is. You should get a bit deeper than that. The important thing is to white balance regularly on the way down. Literally every couple of metres. Cameras don't like to make a big jump in white balance. If you forget then sometimes you can get a "part-way" white balance off the sun at depth and then get a better white balance of your slate or hand or whatever you use (I use the palm of my hand). Once you're past the limit at which it will white balance, just continue with the last setting. Then you'll get to a depth where you might be better just taking out the red filter to let more light in and reduce gain noise. Deeper than that point I typically toggle the white balance mode between auto and manual (the last successful setting I got) to see which looks less bad.
5. Turn on or off the Steady Shot feature?
I leave it on. Others leave it off. Historically people didn't like to use it with housings that were prone to vignetting as the vignetting could change during the shot.
Hopefully someone else can answer your other questions. Have a great trip and do show us the footage!
