Hey Mark,
Yes, "flat" IS confusing. I'm very concrete. When I hear "flat" I picture a plank. Yet when it comes to SEO, you should really envision (and aim for) a short, wide, pyramid-shaped information architecture. You want to keep the most important (money) pages closest to the top of the structure as they tend to receive the most SEO equity and therefore have an advantage when it comes to ranking.
I also agree there's little consistency when you're scanning blogs looking for examples. Blogging is still relatively new and I think you'll start to see more consistency as competition and player sophistication continues to grow.
I like your thought about using topic labels instead of a vanilla "blog" folder; it's the number of topics I'm not keen on. I think a good rule of thumb is to aim for no more than 5-9 pages at the top of your information architecture for the reasons you yourself have observed above. People do search for "wedding blog" and a bunch of other related but similar terms (perhaps one in your niche? "wedding planning blog") so that could work.
I also think your goal of having rich static + variable topic content pages is an excellent one and agree that yes, once you get there, they should definitely be indexed.