You may want to consider a few things such as:
- Avoid keeping guppies with a siamese fighters. Because guppies are colourful, the siamese fighter may mistake it as another male and therefore nip their fins, saying that he could be slightly more aggressive and actually try to kill them.
- Silver sharks can grow quite big and although I have no idea how big your tank is that is 1 factor you might want to consider.
I wouldn't worry about your water change going slightly cloudy, just give it a day or so and it should settle down and be back to normal.

As for the rest I can't really say anything. Good luck with the tank and welcome to the forum. I hope that helps a little bit.