one private key is enough or it should by few of them?
you can import one or many private keys, but it would appear that on Android you can only import keys when you first set up a wallet. I couldn't find a way to import keys after the wallet has been first created.
if I accidently deleted wallet can I reinstall it some how?
If you have the private keys (or seed of the wallet was an HD wallet) then you can recreate (or restore) the wallet by simply creating a new wallet and importing the private keys again (or restoring from seed).
You say you don't have the a seed and only have private keys, so you'll need to import them into a new wallet.