I definitely have character- and movie-related foci. For example, I'm a Frozen collector, but even within that, I especially collect Marshmallow from Frozen, I like just about everything that features him, while Olaf, I don't really collect.
Some movies I really don't collect anything from, but I may see an item from it that I particularly like, and just get that one item. I may end up with a few items from that movie.
My collections can definitely be grouped (Frozen, Cinderella, Little Mermaid, Aladdin, Brave and Tangled are my more-collected Disney movies) but it's not like I feel like I need (or even want) everything from each of those product lines, nor is it that I don't venture outside those product lines at all. A lot of it comes down to the actual item, for example, for the fabric dress princess Sketchbook ornaments this year, I got Elsa and Anna, naturally enough...but also Snow White, because I thought her ornament was so pretty and her colors matched my tree's theme, even though I don't have very much Snow White stuff. Meanwhile, I didn't get the fabric ornaments of the princesses I normally collect more of than Snow White, just because the ornaments themselves didn't do it for me or go well with my tree.
I admire those collectors who have "everything XYZ," those are fun collections to visit. But for me, I feel like I have to have an excitement for each item I buy on its own, I can't justify buying it just to complete a collection (an exception to that is my Frozen Panini stickers because I feel that it's a bit like puzzle pieces of a single item, a complete Frozen album. I'd really like that. But if I can't end up completing my album, that won't drive me as crazy as I know it would drive some people).
In order not to end up having a clutter of visual "stuff", I don't take out everything to display at once. I create my own themes to put on display in parts of my home, and those themes are not always strictly within one movie, but they end up having a cohesive look. My fiance has compared my regularly-changing little set-ups/dioramas to toy store window displays