Might be a stupid question but... could I keep a tank with just plants and not have any filtration on the tank? Maybe just something to keep the water moving like a power-head? I would be using ferts and possibly CO2.
You can...but the question is, why? For the challenge? It will limit your fish load considerably. It would be great for a colony of shrimp, a betta or some sparkling gouramis.
I would at least use a sponge filter, myself...
Yes you can - google Leiden Aquarium (for the Dutch city Leyden) and who'll get a lot of hits on how to set-up and maintain one. But remember in this type of aquarium the plants are first and fish (what few there are) are secondary