A fuzzy dwarf would do super well in a 4' setup like a 55 gal. In fact, you could keep a M-F-F trio or mix a couple of other Dendrochirus sp. into the stocking list. Fuzzies and D. barberi are both sexually dimorphic/dichromic, so they can be sexed. However, D. zebra and D. biocellatus can't be sexed, so you're tossing the dice trying to pair them up. We currently have a male fuzzy and a female barberi in a std 60 gal along with a red-fin waspfish, a cockatoo waspfish, a trio of H. borbonius anthias, and two small scorpionfish (Scorpaenodes caribbaeus and S. littoralis).
As for an eel, I'd look into getting a dwarf golden moray, which only grows to about 12". They're a bit pricy, but the species would be a much better tankmate than a SFE. Once SFE's get some size on them, they have a tendency to get pretty aggressive (I kept one for 15 years, so I've seen it happen).
Another "eel" you might consider is the Green Wolf Eel (Congrogadus subducens), which is often referred to as a blenny, but is really a species of dottyback.
HTH