There is no way to "negative boost" CDI (Central Discovery Index) resources so they appear lower in the search results. The boost feature only applies to local catalog records. One way to make it clear to students which results are book reviews would be to change the label for "Review" to "Book Review" for both the facet and the search results. The codes that need to be changed for the facet is "facets.facet.facet_rtype.reviews" and for the search result it's "mediatype.review".
DOAJ is now CDI-only, so there is no way to delete select journals. Since it is CDI, it is also not possible to "negative boost" the resource.
By default, citation styles will automatically update in Primo VE once the style is updated on GitHub. Here is a how-to for checking which is the current edition on GitHub. MLA and APA have been updated to the current editions.
Although the citation style will automatically update, the label will not. Here is a how-to for updating the citation style labels.
If you want more than one version of a style available, you would have to add the previous version separately. For example, here is a how-to for adding APA 6th Edition.