Hi,
You can alter the button text using the ‘Button Text’ field when you create/edit a product. There is a screenshot demonstrating this field in the documentation below:
You can simply choose a thankyou page that relates directly to that product by specifying the page URL. Could you possibly use that method rather than having one generic thank you page? https://s-plugins.com/customize-the-thank-page-message-of-stripe-payments-plugin/
For your third question:
{purchase_amt_curr} = The amount paid for the current transaction with currency symbol. Example: $1,000.00
{item_price} = Item price. Example: 1000,00
These definitions can be found on the following page:
– Regards Chanel