Hi,
1. The text of that popup can be changed with translation overrides:
www.hikashop.com/download/languages.html#modify
The look of the popup can be changed with CSS:
www.hikashop.com/support/documentation/1...ize-the-display.html
You'll liekly first want to edit the settings of the HikaShop cart notification plugin to increase the display duration of the popup to have more time to analyze the classes of the elements of the popup to be able to write your CSS code.
2. In the settings of the HikaShop cart notification plugin, you can make the popup clickable and it would then redirect to the checkout.
3. That's possible by configuring the HikaShop cart module to be displayed with the "mini cart" in "dropdown" mode. So check the settings of the cart module.