You buy 50 shares, because in your proposed strategy you want to make money whether the stock goes up or down. Because the option strike price and underlying price are the same, the appropriate ratio of underlying stock to options is about 50% if you want to be neutral to the future direction of the stock movement (delta-neutral as they say).

If you bought 100 shares with 100 covered, then you are purely betting the stock is going up by more than the option price. You would break even at $107, but lose on anything lower.

Implied volatility is the amount the stock is expected to move as implied by the price the market is charging. Sometimes it is easier to think of an option price in terms of volatility rather than raw dollars, especially when you are making trades of the type you proposed.

In the Netflix case, the current price of the option "implies" that the stock will move plus or minus 3% per trading day; if it moves more, say 5% a day, you are likely to make money.

Of course, thinking of options in this way also means you are on board with a ton of assumptions in modern options pricing theory, and lots of smart people point out flaws and objections.