I ended up adopting the excellent Scarlett template and, seems this kind of template cannot be edited with the blogger layout designer, I had to spend a good deal of time customizing it without breaking its integrity. Still, I kind of reached my limit in HTML editing and now feel a bit stuck with some details I just can't fix or control the way I'd like.
Now with the official arrival of the Template Designer in Blogger, this might change. I'm considering adopting one of the sample templates and work from there to obtain a result quite similar to the current design, but with the advantage of having more control over my layout and less time to spend editing the HTML file.
Definitely a big step ahead for Bloggers.
See this video for a quick overview.