depending whether you are using the full registration or the short registration edit the webassist/plugins/registration/registration.php or webassist/plugins/registration/full/registration.php
find the following line:
header("Location: ".((isset($_GET["accesscheck"]))?$_GET["accesscheck"]:"users_profile.php?reg=1") ."");
and change it to:
header("Location: ".((isset($_GET["accesscheck"]))?$_GET["accesscheck"]:"index.php?reg=1") ."");
this will redirect to the index page when registration is complete.
Power store is already set to send an email on registration.