Interesting question....
First and foremost, if you want something that will replicate the SmugMug layout, you should use SmugMug. I'm not being facetious. Just stating what should be obvious.
I'm not overly fond of that layout, with groups of thumbnails and slide images jostling each other for screen real estate - it seems cluttered and confusing. You certainly won't find any jAlbum skin that would do that.
Virtually all jAlbum skins follow one of two models. Most are "page of thumbnails, clicking one takes you to large slide image." There are a few that are "all slides, perhaps with a thumbnail strip that the visitor can hide or reveal."
The most common model would be well-suited to your collection. I would organize the album project with a folder tree of varying depth. The top level might be by country - U.S., France, Germany, etc. Then, just following one branch, there would be subfolders under U.S. for Definitives, Commemoratives, Air Mail, Parcel Post, etc. Under Definitives, you might have further folders for each decade. Maybe one for just the Washington Reds!
Each branch of the tree can have a different depth - no need to further subdivide the U.S. Air Mails, for example - there aren't that many.
Beyond that, it's a matter of looking at the available skins to see what appeals to you. Sample albums with multiple layers of folders are uncommon (because they're laborious for a skin developer to create, update, etc.), but remember that almost all skins can handle an almost unlimited depth of folder nesting.
For the bundled skins, there isn't one site to take a look at all of them. It might be easier to create a simple test album with a few folders, each with a couple of dozen images, then make the album using each of the bundled skins, with its default settings, just to get a feel for what they look like. Remember that the customization options are very extensive, so don't worry about things like colors, whether the thumbnails are a fixed shape or not, and so on. That can all be changed.
I've got a site to showcase all of my skins:
https://jefftucker.jalbum.net/skins/
Most of the examples don't have any folder structure, but here are a couple that do:
https://jefftucker.jalbum.net/skins/neptune/folders/
https://jefftucker.jalbum.net/skins/saturn/folders/