I created a sample. The home page of steveposts is the Welcome page: http://steveposts.wordpress.com. Under the full size gallery of photos there are two test thumbnail size photos: Gallery 1 and Gallery 2.
At present only the thumbnail for Gallery 1 on the Welcome page links to a corresponding second level page. The URL for that second level page is http://steveposts.wordpress.com/welcome/gallery1/
On this Gallery 1 page there are several photographs up top for display purposes only, with text. Scroll down for two thumbnail photos that link to third level pages, respectively titled 'Series One' and 'Series Two'. At present, only the thumbnail link to Series One is operational.
The URL for Series One (the sample third level page) is http://steveposts.wordpress.com/series-one-spring-67-antiwar/
This page has three thumbnail photos; each will link to a corresponding fourth level page, and that will be it, with respect to levels below the Welcome page.
Question 1: You ask, Do you want the URLs of the pages to reflect the hierarchy or not? Yes, so I can provide optional links for the user to go directly to a sub-level page. And a menu that lists the hierarchy would be good to have at the bottom of the Welcome page. (Before I didn't think that would be necessary, but now it probably would be important to have.)
Question 2: How do you get images uploaded separately to line up in a horizontal row, centered or aligned left?
Note: In most cases on these pages I am trying to duplicate a thumbnail style gallery. If each image in a thumbnail gallery I created could be made to link to a corresponding page, then I'd do that. But I don't believe that is possible.