A R.O. unit is for treating your tap water, not to be used as an aquarium filter. It is a great idea to use R.O water for aquarium use but it can not be used straight, you must add back to it the needed trace elements & minerals needed for specifically what you are keeping in your aquarium. In many cases, your tap water treated with a good quality dechlorinator will be fine for a large number of frequently kept fish.
As per the U.V. sterilizer. They are a good tool for decreasing parasite out brakes. Thier are espcially usefull on sensitive or problematic fish such as Discus or Saltwater butterflys or tangs. If your keeping fish that are not parasite prone (african cichlids for example) you may not have a need for one.
A wet/dry type filtration system is hard to beat in terms of processing waste. They are very efficient at rapidly breaking down ammonia & nitrite and they are great at de gassing (oxygenating) your water. Very easy to maintain too. I'm not a big fan of canisters because thier ability to process waste is limited because of thier size and they are not conveinient to maintain. A typical system should have it's prefilters rinced every week or so, I doubt canister owners break open thier canister every week to rince out the dirt trap in them.
Fluidized bed filters are effecient biological filter too. THe water coming out of them often is low in disolved oxygen so additional aireation may be needed with thier use. If you wanted to use one in combination with a wet/dry, there are "hang on" models and stand alone models that can be put in or on the side of your sump. Rainbow Lifegaurd makes a nice model for this type of use.
Hope this helps....
Joel
