photo tab images not in media library

I have 2 questions….

1) if a site grows very large, say 1000 different listings, and each listing has 9 or 10 images in the photos tab and a featured image, would a directory site be bogged down even if only a few images were being viewed simultaneously, or does the total number of images on the site determine the site speed?

2) But now I have an additional question…I went into the media library to add alt tags to my images at the suggestion of Yoast SEO, and I noticed that only the featured image on most listings was in the media library, and none of the images in the photos tab were in the media library. I am somewhat of a newbie, and I thought every image on my site (moonshinenetwork.com) would be found in the media library. Since I bulk uploaded them when I created the listing and they are viewable on the front end, where are they being drawn from?

Sorry, I’m sure this is a very basic question but I’ve never run across it until now.