Rob,
A few things to keep in mind...
My fishroom is also rather small at 9 feet by 6 feet. It was originally the maid's quarters, but I consolidated by getting a wife (Thank goodness Erica does not read the Forums!

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Centralized heating is a good idea. I use a 1,500 watt room heater and like it a lot. The top tanks stay at 80F and the bottom tanks in the mid-70s (with the exception of the tank right next to the heater). You will find that the heat variation between the top and bottom levels work well as you can keep tropical piedmont catfishes or North American madtoms in the bottom tanks and lowland cats (like Orinoco or Amazon fishes) up high.
My recommendation would be to stay away from centralized filtration for several reasons.
1) It is a lot of work to build (although fun as well)
2) Disease! (enough said)
3) All tanks will be the exact same temp, stopping you from keeping several interesting catfishes.
4) They take up a lot of space that is key, especially if you only have a wee fishroom (rather have a 55 gallon tank or 55 gallon sump?)
5) Forget spawning anything since you can not modify the chemistry in one tank alone nor can you change the temp in one tank alone.
If you were raising/breeding nothing but Discus it would be a great system. However, what happens when tank #1 has ick, tank #2 has some
Corydoras that you want to zap with cool water for a spawn and tank #3 has several
Chaetostoma that need cooler water?
Another suggestion is to stay away from any and all air driven systems. I love sponge filters and the like but finally got rid of them all a couple of weeks ago. Air pumps all eventually get very loud and running the tubing all over gets old. Even a slightly noisey airpump will sound like a train in a tiny fishroom. It might work if you could keep a small blower outside, but then we are talking a fish house and not a small fishroom.
Use tight lids on all the tanks to keep the humidity at bay.
Use wrought iron for the stands as it takes up far less space than wood.
Keep your electric cords off the ground!
Some views of my fishroom. Barbie might just note a certain cave she gave me recently.
The ten right next to the heater stays pretty warm at around 82F.

"My journey is at an end and the tale is told. The reader who has followed so faithfully and so far, they have the right to ask, what do I bring back? It can be summed up in three words. Concentrate upon Uganda."
Winston Churchill, My African Journey