Just use a similar Text-Editor as we already have at the User-Profile.Pages.
If you are not an experienced XenForo-user, then it is a bit hard to figure out how to write a review.
You first need to figure out that you have to click onto the "Stars" in the sidebar (which opens a popup) in order to enter your Review-text.
It would be much more logical to directly visually display the Text-Box for Reviews.
Of yourse you are only allowed to write Reviews (enter any text) once you have downloaded the Resource, meaning "Review-permission-options" stay the same as they currently are.