Momentum Template: Need capability for Image Grid Block for single light box and auto images (or equivalent support)

I'm using the Momentum template for my website: https://earthworm-mandolin-xeek.squarespace.com/new-page-horizontal-masonry

What I want to do:

• have a single image block that I can upload several images at once.
• the block of images are not all of the SAME size. Preferably Auto-Size or I can manually tweak as needed.
• the single block of images have ONE lightbox for all the block e.g. you can scroll and naviaged through the images once you've selected one.

Options I see with this template that is not working out.

• Horizontal Masonry page. Issues: 1) I have to upload each image one at a time. 2) I can enable the lightbox per image but not for all the images on the page to be tied to ONE single lightbox. Plus: I can manually tweak the size of images and move around individual images creating my own image layout where images are not the same size.
• Image Grid Block (added to a page): Issues: 1) All images are the same size with this template - there isn't an Auto Ratio option or an ability to tweak and move around images within the grid block. Plus: 1) I can have ONE single lightbox so once an image is clicked, can navigate horizontally through images.

Is there an option with Momentum template that can do what I'm requesting either through Site Style or Custom CSS.

Also, I would like to make this image grid layout extend the full width of my browser page / mobile page. As you can see from the URL above: It only goes to partial page.