Lovely setup!
As far as I know, Puffers are a DEFINITE NO NO and the shark is a risk. The crayfish will need something to hide his whole body inside whwn he has moulted for a few days until the shell hardens. His whole body would need to be out of reach and there isn't anything in your tank where that can happen that I can see, he would still be exposed! Getting more than 1 crayfish is also very risky as they are territorial and will likely fight until 1 or both are dead unless they have A LOT of room (even then it is risky)! I would think your tank would only support the 1!
Fish wise you would want peaceful mid to top dwellers so they are as out of reach as possible, but the crayfish is an opportunist so there is always some risk. Tetras fall into that group and there is a wide range of sizes to suit most requirements?
Simon