What's a fruit tetra? I don't think I've ever heard of that species. Please make sure you know what you're buying (ie scientific name) because common names can cause a lot of confusion and problems. All tetras are schooling fish so should ideally be in a group of a minimum of 6-8 fish.
Guppies are generally OK with tetras but watch out for fin-nipping.
A Black Moor is a kind of goldfish, which is a cold water fish. They don't thrive in tropical tanks and they are extremely polluting. Goldfish need about 10 gallons each to be healthy.
For tropical fish the general rule is one inch of fish per gallon of water, however, the larger the tank the more stable it tends to be (in terms of water quality). I personally wouldn't have a tank smaller than 10 gallons - you can pick up a complete set-up from yard sales or Ebay.
Before you get your tank please follow the link in my sig and read about cycling and how to avoid "New Tank Syndrome".