1. Please use WHMCS Bridge Plugin to connect between both WordPress with WHMCS. Please watch the video tutorial https://youtu.be/AlPJOLmGwLI to configure the WHMCS Bridge. Moreover, watch the video tutorial https://youtu.be/U6QHglSbaOk to setup Domain page Integrate with WHMCS. Also, watch the video tutorials https://www.youtube.com/playlist?list=PLbmIKrgYlRbpUN1Y2pG2-cqTdXgvUlW6d to customize the theme in a proper way.
2. You will have to create all of the prices, promotions, products, services etc. on both WHMCS & on WP. After then, you need to update the buy now or other WP links with WHMCS. That means, you need to use WHMCS links to WP to connect all of the WHMCS services in WP. This is because, when a customer will click on the buy now link of the website, then the customer will redirect to WHMCS for register/checkout/billing.
3. You need to use WHMCS links to WP to connect all of the WHMCS services in WP. Then, when a customer will click on the buy now link of the website, then the customer will redirect to WHMCS for register/checkout/billing.
Please Note: here the WP is to represent the services and WHMCS is for billing/client area/support.
Thanks for your understanding.
Best Regards,
ThemeLooks Support Team