Im a begginer tank owner wondering about how many shrimp i can have

That depends on the starfish. Many are specialty feeders that eat only one particular thing (crown of thorns for example). I don't know anybody who knows exactly what linkia starfish eat. It has been suggested that they eat biofilm and maybe some algae because they don't seem to do well in new tanks but I don't think that there's any "real" data out there as to what their diet consists of. If anybody knows of any, however, I'd be interested in hearing about it.

 

Just to add my chocolate chip starfish eats half a green mussel once a fortnight - covers it over completely so even my hermits dont get a look in -and when he/she moves away the shell is spotless