Hi Lija, just found your new thread. Did you ordered the custom tank yet? Is it cheaper that way than just buying an ExoTerra Large Medium (36x18x24 in tall)? You could place a 36x18 in. piece of 3/4 in. marine plywood on your stand to hold it with a 3/4 in. trim glued to edges so it's nice.
In regards to your question on pond or filter; suggest you look at the Supreme Danner Ovation internal filters. They are nice units that output to a tube that could be connected to hoses, same as a pump. They go from linked unit (1000 and largest) then to 700 and 210 models.
If replacing tree fern with coco coir, recommend using the chunk coco; not the shredded one. Good luck!