I forget which size, but there is a Sullivan round tank that is a perfect drop in replacement for the stock tank. In my opinion, saving $8 is not worth the worry.

I think you'll like the Avistar, I picked up a used one and it flies pretty well and is relatively aerobatic with the semi-sym wing. Will fly inverted easily. One mod I recommend is to swap the single aileron servo for two and use flaperons if your radio will support it. It makes a noticeable difference on approach speed.

Duke