Ever thought of opening membership up across state lines? I know that may sound nutty, but in central NC there are no aquarium groups anywhere. It is very disappointing to say the least for me. I would love to be a part if a group of like minded aquarists.:)
I would do the plywood platform on the solid base. Your support must be on the corners. If your tank springs a leak it will be at a corner over 90% of the time. The plywood will support the siliconed corners/joints.
You can't over filter your water. Filtration is the name of the game. The more BB colonies you have the healthier your water will be and fish. Alternate filter maintenance and you won't be over working yourself. I run two filters on all of our tanks.:)
After filling your canister with media components your gph is going to be cut in about half. Which would be about 157 gph. That would only turn your water over about twice an hour. All I have read says 3/4 times for optimal results. I personally have a canister and a large hob on my 75...