Hi @ztavel, I do know of people doing Masonry for CMS items but not for Gallery images, just yet.
Everything you are talking about is possible, just not with Webflow at the moment on static pages.
In a CMS page, you can get away with this and it does work.
Here are some links for reference:
Masonry layout: [Beginner Tutorial] Masonry Layout using masonry.js
MixItUp: MixItUp w CMS masonry layout issue
Masonry Grid: How can I create a masonry-style grid?
Try these, see if they work for your scenario. However, keep in mind, CMS-Gallery only works on CMS Template Pages!
Good Luck and Happy Designing,
Brandon