One of your most powerful methods of showing data, within a fully controlled manner, is using the combination of global fields and portals.
The portal object isn't simply for showing the related data as it belongs to one single record. A portal is a display tool useful for presenting whatever data you want and, however you want.
In this video, I use the example of showing multiple events based on the selection of multiple locations. Whether you need to provide a simple multi-selection option in your UI, or your filtering needs extend to multiple field values, the use of a global field, in conjunction with a portal object, is how you can achieve a lot of your display objectives.
Click the title or link to this article to view the video.