Hello,
01. You can add post tag filtering in the sidebar area of your gallery page.
Please navigate to Appearance > Widgets and add the Tag Cloud widget (or “Post Tags” widget) to your Main Widget Area.
This will allow visitors to filter posts by tags directly from the sidebar on your gallery page.
02. You need to upload images of the same size and proportion to show the blog design in the same size.
Also, your column height depends on the amount of content in the blog.
Best Regards,