Hi @rixbea,
Thank you for your purchase.
In this doc, we've described the steps on how to install the "wpForo User Custom Fields" addon, please check it out.
https://wpforo.com/docs/root/addons/wpforo-user-custom-fields/addon-installation/
The other add-ons can be installed in the same way.
Also is it possible to run wpforo independently as a forum site with its own domain or do i need to add it as a plug in to a blog or website ?
If you're using WordPress multisite you can install the wpForo with its addon on one of the subsites and use it independently of your blog.