I have a small 80 gallon stock tank in the backyard with just one bass in it. I can tell you from experience that you are probably going to want to get some biological filtration as had been suggested.
I was using just mechanical at first, and it was "working", but the water was very very dirty, and ammonia / nitrate levels were higher than I was comfortable with. I had to do a lot of constant water changes. Keep in mind this is with just ONE bass.
The water started to clear up when I added biological filtration. I basically stuck a lot of nylon sponge things (i don't know what they are called...) into the filter box to serve as the biological filtration media.
I would actually get a few fish and go with your proposed plan. Make sure you have your system up and running a few weeks before you even put any fish in it (or however long it takes for the tank to cycle).
Your plan will probably not work out exactly how you have imagined, but I think you should go ahead with it. I learned a lot from "failing" (kind of a harsh word) the first few times, but who knows, your system might work!
I would normally say that life is too short to make "mistakes" others have already made, but I think this is a valuable learning opportunity for you.
Have fun with it, and keep us filled in with how things progress.
