How far out an expiration date should be (Less than a year though) so that time value has minimum impact and Gamma is high...? And the second question is.. any particular things to keep in mind when trading an equity option vs. an index option?
Check out the chart below. It shows the gamma and theta profile for ATM AAPL options with varying maturities going out to January 2017. Essentially, to maximize your gamma, you want to minimize time and maximize proximity to the underlying price (closest to ATM as possible). The left axis in the chart shows each option's gamma, and the right axis shows each option's daily theta as a percentage of the option's price. Gamma tends to flatten out after you get 3m+ and theta flattens out after 1m. Which maturity you go with depends on how much time risk you're willing to take to get more gamma.