I have moved your post into an appropriate thread. Work your way through the list in the Wikipost, and many questions, including some that you have not yet asked, will be answered.

Most likely American Express will automatically give you a pro-rated refund of the Business Gold annual fee, and bill the full Business Platinum fee.

You will earn bonus points for travel only if you book through Amex Travel. This applies to airfare, hotels, cruises, anything. There is no bonus for using the card directly with the merchant.

Read the Wikipost of this thread to be sure you understand how the 35% pay-with-points rebate works:

https://www.flyertalk.com/forum/amer...35-refund.html