There is no general rule regarding the number of murits (idols) of Hindu Gods that can be worshipped in a puja room. There are puja rooms that have murtis of Ganesh, Shiva, Vishnu, Krishna , Devi etc. But there are some rules regarding the number of murtis of the same God. This is especially followed in North India .
A puja room should not have two Shivling, three Ganesh murti, two Shankhs or Conch, two murtis of Surya (Sun God), three murtis of the same Goddess, two gomati chakra and two shaligram.
Usually, right handed Shankh is used for worship.
Damaged murtis are also not worshipped at home.