GoPhone Hotspot data expiration questions

I have a new GoPhone account for my new mobile hotspot.

The Plan renews May-23-2015 and the Current Balance ($0.00) expires Jul-22-2015.

I’m unclear about Plan Renewal date, Balance Expiration date, and how the balance is allocated.

I have 3 questions:

1) If I refill my account with $100 Jul-21, will that reset the expiry date to July-20-2016?

2) How much data does this $100 buy?

3) How long do I have to use this data, a year?

Thanks.