W/o owning a stock can I sell options of that stock and how many I can sell ?
Yes, you can do shorting even without holding the stock with you. Long/short will totally depend on the funds that you have in your account. For selling margin is required, to buy premium amount one should have, the premium is calculated as lot size * price. You can go through the varsity module Options Theory for Professional Trading for better understanding.
To know the margin required, you can check here