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Help with CMS gallery trick in Webflow

Hi Guys,
So I have just finished designing this ( amazing work around on my site but I am slightly confused.
I am sure it is a very easy solution.
If I am using this CMS gallery but want the photos to match the page, (as of course, every page is going to have to hold different photos) how can this be done? Collections are limited to 20 (40 business plan) so does that mean i have to limit my project like webflow limits our designers?

Thanks for you help in advance.

Here is my public share link:
(how to access public share link)