Yes, goldfish are very social and love to be with other goldfish. As long as one is not small enough to fit into the other one's mouth (goldfish will also eat just about anything), they will be fine. Goldfish are typically not aggressive unless it's a male chasing a female for spawning purposes.
A word of caution: Goldfish create LOTS of waste so you don't want to get more than your tank can handle else you will not be enjoying your goldies, you will be doing water changes trying to keep them healthy. A good rule of thumb for goldies is 20 gallons per fish, to give them room to grow in good quality water.
goldfish do not live on land
Your goldfish will not live "longer" no matter how many or how few you have.
For househeld goldfish, they generally live 6-8 years
yes
No, goldfish are freshwater fish.
depends, can a ten gallon tank live in a goldfish
No, goldfish are best with goldfish. In addition, tilapia have different needs and are quite likely to be aggressive towards the goldfish.
A goldfish is a freshwater fish, and as such does not live in the sea.
no the goldfish would it the tadpole
Goldfish are egg layers
No
No