Just because fish are growing doesn't mean much. I have seen goldfish kept in bowls that managed to grow large enough where the bowl had to be cracked open to get the fish out. I wish I was kidding!
I'm not saying you're a fish abuser or anything, it just sounds like you need to do research before picking out which species you want. I know it's hard when you see a beautiful fish at the store but it's in their best interest
. Had you researched, you'd have known that puffers are notorious for nipping and bullying other fish. You'd also have known that the crabs aren't freshwater (the puffers probably weren't, either, by the way), need land, and are escape artists. Even just a few minutes of Google searching can go a long way!
Your fish are alive and doing ok because you have chosen very hardy species. That doesn't make the set-up appropriate. All I'm trying to say is be careful and research in the future--it would be awful for you to end up coming home with a fish that kills all your other fish or something
. I would also be prepared to separate the fish if needed. Goldfish are usually ok with smaller fish such as the barbs when they're young but can be bullies as they get older, for example.
Honestly, if you really want what's best for your fish you'd separate them into two separate tanks. One large coldwater set-up and a smaller tropical set-up. But if you can't do that, at LEAST have a small tank ready for separations (you should have a hospital/quarantine tank anyways, they're really handy and cheap to set up).
By the way, I hope you're aware that your goldfish have the potential to get REALLY big.
I mean REALLY big.
They're fine in an aquarium right now but one day you might need a pond
. You happened to pick the largest goldfish--common goldfish.
Once again, I'm not trying to be rude or anything, I know you mean well and care about your fish. The tank seems large and clean, your goldfish aren't in bowls, etc. But I do think you should read up on the species you have before you have another puffer incident