The live rock and live sand should handle all of your filtration once the tank has cycled. Wet/dry trickle filters and bio wheels support the bacteria that break waste down into ammonia, then nitrite, and finally into nitrate, but no further. Wet/dry technology is fine in the fish only tank, since nitrates do not have much of an effect on fish. The bio-wheel is a type of wet/dry filtration method, and wht happens, much in the same way as bio-balls in a trickle filter, the final nitrate by-product stays in the system.
Reef tanks require water parameters with little to no nitrate. LR and LS break down the nitrogen cycle well, but some "export" method for the additional nutrients may be necessary. Whether thourgh skimming, water changes, or macro-algae trimming.
For a little more insight on your smaller tanks, check out the nano-reef forum here on Reef Central. Most of the folks there have tanks 20 gal & under (actually a majority of them are 10 gal & under), they are running skimmerless with more frequent water changes & are continuing to have success with good water quality.