Yeah, unfortunately Galleria can be a bit finicky. I've had trouble with it myself so I can't take money for the work. You may want to find a Galleria expert or developer. Sorry. I can't help more. Make sure to read the other problems people had on this thread in case they solve your problem.
great tutorial! Very easy and simple! I did evertyhing you said and the images ahow up next to each other and not in a gallery :(
Did you maybe find a solution for this?
My shopify theme was customized by some other experts but I do not see why would that interfere with the look of the page...
If you did not find a solution - could you maybe take a look at the website I am making?
You'll have to check Galleria documentation for these answers. For the size, you can just change the size of the images you're using I think. Galleria does have a caption function as well but you'll have to check their docs for that.