When you integrate Wishlist with eStore it does everything through the PayPal IPN (Instant Payment Notification) feature. This also allows the integration with the affiliate software for commission awarding purpose. When you use the IPN feature everything starts to happen in the background as soon as the customer hits the "Pay Now" button on paypal.
So after a visitor pays for a membership they will receive two emails from eStore.
1) one for the standard purchase email.
2) and a 2nd one which will contain a unique link to complete the member registration.
once the visitor clicks on this unique link they will be brought to the page where Wishlist will let them complete the membership.
Due to the limitation of the integration process you can not choose the option whereby the customer is sent back to the site to complete the registration after the payment (the customers will have to do this part by following the unique link that is sent to their email after payment).
You can customize the "Return URL" in eStore's settings page so it redirects the customer to a "Thank You" page after payment where you can put general instructions for the member explaining what to expect/the next step (eg. you will receive an email shortly ...)
The WP eStore and Wishlist integration instruction can be found at the following URL:
http://www.tipsandtricks-hq.com/ecommerce/?p=448