do you need to have balance for wallet mining ?
No balance needed.
Hi where can I find my current hashrate?
And calculate income daily with cpu? Mine is i5 3650, I have 3 computers so I copy the same wallet file to 3 computer to mine for 1 wallet right?
Realistically you will be better to wait for pool mining.
You can find your and network hashrate by entering getmininginfo on debug console.