Ryan,
I would put a lot of my effort into figuring out exactly how to build and hang this tank. Acrylic seams will not always hold under the stress of hanging the heavy salt water off of the floor. Also, you need to think about what things you want to keep in the tank, so that you can plan on how important things like a DSB and an automatic top-off system are going to be for your tank. I must admit, I am coming of as a little more down on this idea than I really am, and I think that is because as we speak I am repairing a DIY tank (I did not build it, I just maintain it) that should be holding my bimac. The bottom seam broke under the stress of the water, and I now have to find a new way to support the tank while my bimac waits impaciantly in a 1000 ml beaker.
On the other hand, I think that your idea is really cool (sorry for the above venting, sometimes I just need to blow off steam). Please make sure that you have a good support for your wall tank to rest on, as well as a brace around the top of the tank. I would even concider anchoring the tank to the wall and then mounting the plasma shell over it. Remember that seawater is heavy. Also, remember that you are not limited to a reef. I have been iching to set up a little kelp forest echosystem that would house sea horses. Macro algea and live rock could work as the primary filtration, with periodic algea harvests for nutriant export. Not much flow would be needed for a system like this, and with no coral, you would not have to worry about compitition from the macro. That is just one idea.
The other idea that you should look into is a sealed tank, (preferrable without the sea horses, which won't appriciate the lack of gas exchange in a sealed system.) Check out this link in the nano section.
http://reefs.org/phpBB2/viewtopic.php?t=17395
It was started by a guy named brandon429, who rules the realm of sealed tanks. This idea of yours sounds right up his alley, and he might have some great ideas on how to set up a great sealed plasma tank, especially if you are not planning on having any fish. Good luck, and post lots of pics.
Mike