Crayfish for my Local monster tank?

hi folks,

i got 2 3ft tank and wanted to setup a "Local(singapore) monster tank".

the fishes i want to keep are:
1) 1 walking Catfish - "TORSAT" - 20cm
2) 1 dwarf snakehead - 20cm
3) 3 Giant Pikehead - 18cm
4) 1-3 Climbing perch - 25cm
all are predatory fishes.

i was thinking to make the tank more interesting by keeping some other "ODDBALLS" and came up with the idea of crayfish etc...
i dun think frogs or newts can survive in this monster tank LOL!
and turtles dirty the water easily.

any interesting freshwater crayfish, crabs, shrimps, snails to recommed for this type of setup?

how large do those crayfish in LFS grow? is these crayfish dangerous to my fishes?

thanks