no it can not because it may give the turtle disease
You should not have goldfish and platies in the same tank ever.
YES, you can put a map turtle in the same tank with a slider.
Does your snail have algae on it? Goldfish will eat anything that "grows" in the tank. They will eat turtle droppings, water scumm, algae, anything! That is why they are called bottom feeders.
I am unaware of "Black Spot" being a disease of fish. So I would say no.
yes, but it may kill the goldfish
no
Rule of thumb is to not mix tropical fish and goldfish.
No, Neon Tetras and Goldfish do not belong in the same tank. Goldfish prefer cold water, while Tetras are more of a tropical fish.
Depends on the temperature
Of course!
Yes, but your tank size needs to support it. If you mean that a regular goldfish is a long single-tail goldfish, then you need at least a 40 gallon tank just for the 2 fish due to the size potential of the common goldfish. If you mean a regular goldfish as in a round bodied fantail, or perhaps a ryukin, then you need at least a 30 gallon tank for the 2 fish.
It's a possibility, but a goldfish and a platy should never be in the same tank as they are not compatible, and their needs are different