1) Assuming atleast a few months of time remaining until expiration of the option and because of the approximate "50" delta of the option, the option premium will fluctuate only half as much as the stock when the stock is close to $50/share, i.e. at-the-money. Two put options will "more precisely" hedge the 100 shares of stock instead of just one put option. As time elapses, the delta will increase and also become "jumpier". In the days leading up to expiration of the option, one contract becomes sufficient to hedge as the delta approaches "100".----basic knowledge....
----fine details about options.
----1 x atm put = full hedge of 100 x shares....
----people say you need 2 atm puts to be hedged.

2) The one option versus the 100 shares is fine as long as you make no adjustments before expiration of the option or until the shares are sold. Your position is said to be static, hedged or a "married put".