Keep in mind that "bioload" is simply the ability of your tank to process the waste produced by livestock. At this point in time, if NH3
have been cosistantly zero and NO3
is low your tank's biofiltration is processing the bioload just fine. You may be able to squeeze one more small fish in but that would be max. There is just not enough realeastate in there to house too many fish (more stocking related then bioload related).
As for corals, most do not contribute directly to the bioload of a tank. Some corals can indirectly contribute due to special dietary needs (filter-feeders for example). The list you are considering should be just fine. They will tend to grab food from the water colume at feeding time.
The yellow clown goby is a great nano fish and one of my favorites. However, they are very timid and can often times be "bullied" out of food by more active tank-mates. You can give it a shot, just make sure it gets some food at feeding time.