Welcome to WebmasterWorld Victor!
While Luibokoretti's ideas might help with promotion, they have little to do with your actual question.
I don't think URL structure is that important for usability - most studies I've seen show that the vast majority of users never attempt to edit a URL. All of us geeks here do it every day, but studies of regular users show that in most studies they don't see a single user navigate by editing URLs.
That said, I do think of it as an added breadcrumb for the savviest users, and of course it supplies a relevancy signal for the search engines, so I think it still has value to get it right, just that its *usability* value is limited. So I would think of that more in terms of SEO than usability, though others might differ in that opinion.
Sort of an aside and it also doesn't really make a difference, but if you're thinking about URL structure from the ground up, I'd drop the .html - serves no purpose and just complicates things if you change technologies.
Back to the question at hand, there are a couple of things that I might think about.
1. Include some type of search. This looks like it could be a large catalog and, users these days expect some sort of site search. It's a primary navigation on mega sites like Amazon. The simplest thing is to include a Google custom search widget.
2. Search is fine, but search forms are, of course, not crawlable and some users will want to drill down. So clearly you need a good navigational structure that is usable to both search engine spiders and users. So the "solid internal linking structure" you mention is key for the SE, but search engines and users still have somewhat different needs (e.g. SEs can digest larger sets of randomly ordered links than a human can).
Old rules of thumb, taken out of original context and applied too mechanically, commonly resulted in advice that said for human users you needed to keep things within two hops of the front page and present lists of no more than seven items, but these old rules are poor guidelines to apply too broadly for several reasons.
- most users won't land on your home page anyway, so it's key to think about how they'll get from the page they land on to the page they want - it sounds like you have a plan there already with the solid internal linking
- the size list that a human will digest will depend on a lot of factors. For example, if we're looking for something specific and are presented with an alphabetical list, the number of choices can grow dramatically beyond seven without negatively affecting usability.
- most importantly, it has been demonstrated that you can take users through many clicks - far, far more than two - as long as the "information scent" is strong. They just need to know they are getting closer to their goal at a reasonable pace.
So you have to balance the size of your link listings with the strength of information scent when you're building out navigation for a large number of items that you want hard-linked through your navigation structure.
I'm sort of rambling, but I guess what I'm trying to say is to think not just in terms of URL structure and link structure in the abstract, but to also pay attention to the visual presentation of that internal link structure and making sure that your navigation lists are digestible (using logical and immediately obvious organization principle on longer lists, such as alphabetizing) and provide scent (for example breadcrumbs, so that when someone lands on an internal page, she can see immediately where she is in the hierarchy, how far along the path she is and so forth).
I don't know if that's helpful in any way, or just obvious, but perhaps it will at least get some discussion rolling.