I know mine is quite a bit bigger... but I just added 20 zebra darts, 5 yellow tangs, and 125 snails/hermits and they seem to be doing fine... all parameters are within spec. With a 90g adding 5 small fish shouldn't be a problem.
Although I do recommend that when you are adding a group of fish you use some kind of bacteria. Most company's sell them... Haggen "Cycle" API "Stress Zyme+" and Seachem "Stability"