Yes, but only for a very short time, for goldfish are known to grow rapidly.
Absolutely, in fact I am sure you can fit a few more in there too.
If it is goldfish: 7 can fit. if it is mos other fish (besides koi) you can fit 14
No, 5 gallons is way too small for a goldfish- they need at least 10 gallons each with the minimum tank size being 30 gallons. As for the crab- depending on the species he/she may be able to fit in a 5 gallon tank by him/herself comfortably, but this is usually not the case. Your best bet would be to go with a different type of fish such as a Betta fish- unlike goldfish, they can actually thrive in small tanks.
No, but it also depends on the size of the goldfish. I would say to go pick out 2 goldfish, put them on hold and go back home and see if you think they will fit, if you are still not sure, try bringing the tank to the petstore and ask them what they think.
Depends which tank.
You can fit one betta in a 1 gallon tank, but nothing else.
Yes as long as it can't fit in an other fishes mouth it will be perfectly fine. A fishes tank can never be too big.
You can fit a 5 gallon fish tank on a school going desk.
4,000
Regardless of the type or size of goldfish the minimum acceptable size of an aquarium for a goldfish is 30 gallons. Buy a tank that is at least 30 gallons if you plan to have goldfish. You can comfortably fit 3 goldfish in a tank this size but no goldfish in a tank any smaller. Goldfish are essentially pond fish and need lots of space to swim; they will not thrive in a small aquarium.
No the male will eat them keep them separate them until they can't fit in the mouth of the goldfish.