Can different type of tetra,danio,guppy and platy live together?

Yes, they can and this would be referred to as a community tank. The number of fish you have will be related to the size of the tank, the bigger the tank the more fish you can have. Notice when you buy your fish where they swim in the tank, tetras usually are busy and swim near the top, while guppies seem to enjoy the middle region of the tank. Fish while not out grow their environment, again bigger the tank the bigger the fish will grow. Check when purchasing fish, if it will do well in a community tank, hopefully you will avoid aggressive fish this way. Good luck and enjoy.