1. Usually use mid price =(bid+ask)/2. Because option has really large big ask spread. The last price is just the price of the last executed trade. Some not so liquid option may have last trade several hours ago or even yesterday. So last price is not so good.

2. if option's maturity is less then 3M, then use 3M spot libor. For longer maturiy, bloomberg has S23 curve which is stripped from standard USD libor swap. But you may not have access to this kind of data. So feel free to use 3M spot libor. If you can not get libor, use fed fund rate or 10 yr US treasury yield (which you can get on yahoo finance)

3. usually actual/360, actual/365, 30/360, business day/252 all works. This usually matters much for interest rate derivative. For equity option, just choose whatever you like. The impact is really small. I personally prefer business day/252 for option.

btw, you also need to consider the dividend if you think the stock is going to pay the dividend in the future. And try to use some ATM option to verify because they have a relatively much better liquidity.

Enjoy your play :-)

非常感谢啊，回去找数据看看

谢谢，受教了。