I think Hawaiian Reds are brackish - they're supposed to be really hardy, and will probably be fine short term, but eventually it'll catch up with them.
Both guppies and platies can breed pretty fast, and that could add to the bioload greatly - that'd be my main concern for bioload, actually. The Crystal Reds might notice that bioload change pretty fast, and that'll be bad.
Those would be my main concerns. Bioload wise, the tank is fine the way it is, you may even be able to add more shrimp... but in the future, the bioload may be a bit different.