If I want to have more than one head or have multiple heads will that kind of feature be available in the future or can you have one and only one head?

Currently, your head is set by your name. If you have multiple heads, you will need multiple names.

Some people do play as this, so the choice is yours.

but what about other people being able to see them.

if they have the head texture, they will see them when you have the corresponding name.

I am not entirely sure on how the system works now for submitting head textures, but they are downloaded automatically (apparently).