What's a good plan to make a gallery wall?

Sorry, not sure what plan you are speaking of. I would love to help but not sure what you are looking for.

https://www.potterybarn.com/tips-and-ideas/how-to-create-a-gallery-wall/

Gallery walls are a great way to display your artwork and photos in different sized frames. Lay-out the display on the floor in front of the wall, cut out the size of each frame on paper and tape each to the wall to see how it would look. The photo is an example of what I am referring to. Have fun and be creative with your design and frame styles.

I like to coordinate the frame and mat colors to bring some cohesion to the grouping. Layout on the floor and then begin transferring each one to the wall measuring the height and width to get it on the wall right.

If that doesn't make you confident, then use large sheets of brown paper, number each picture, and poke holes (I use a compass point/metal kabob) in the 4 corners of each picture, and number the space to match. Tape the paper to the wall and use a pencil to transfer the holes to the wall, then add your hanger and put each up as you go.

I guess you could call what we have a "gallery wall" it is our staircase wall. Somehow it evolved into being pictures of women, specifically mostly women's (girls and female babies also) heads. I do not concern myself at all with matching frames. Can be wood, metal, different colors. I rehang things as needed to fit more in. My husband is an artist so some is his work, (like the ballerina shown here) Latest addition is a long forgotten painting of our daughter as a baby, he did. A gallery wall can include anything you like done esp for your own satisfaction and does not have to remain static.