They might have suggested it was overstocked not necessarily based on the number but the size of fish you have. I try to add fish based on their compatibility (with each other and coral), adult size, care requirements, and the environment I can provide them. I’m not sure what kind of eel or fox face you have, but some of them require bigger tanks than 45 gallons (especially factoring in displacement from rocks and sand if you have any).
However with that being said, if none of the animals are stressed, and parameters remain consistent and stable, then you may not have a problem but still be overstocked in a text book sense.
None of this is an exact science (well some of it is, but you get the gist). It’s all based on people’s experiences and observations. Nobody knows your tank better than you do, if you have even a slight concern that it might be overstocked, then it likely is. If so, I’d recommend letting go of a fish or two to a LFS, or upgrade to a bigger tank. (I always prefer the latter, however I too have limited space, I thought my 100 gallon would be the end all be all but truth is I’m still left wanting bigger tanks to have those animals that need the space.)
Hopefully everything works out and you do what’s best for your fish and yourself!
