Wow, thanks -- once again! -- for all these helpful replies, everyone! But y'know what? I think that at this end of things, I'll just stick with that asterisks way of separating the breaks in the poems (which is also reminiscent of how various print versions have done it, too), if only because it's just so much simpler and less problematic.
And re those "preview consoles" in both Sigil and Calibre, I took a look at both (it took a while for me to find the one in the latter!)

and yikes, I think that's complicating things too much for me! "TMI", as the kids say (ha ha), and I seem to manage okay just working on things as I do.
I suppose I'm pretty much done now with my query here -- and it has indeed been very fruitful and informative for me, and I hope it has been (or will be) for others, too).
I do have one other quick question (which I presume has a simple answer) related to this Walden ebook that I've been working on, which I hope I can just toss in here without starting a new thread -- if I should do so, though, please just let me know.
When I started this current ebook, it was just going to be Thoreau's "Walden" and nothing more, but now that I've been working on it for a while, it would appear that it's becoming more like "Walden & Other Writings", with various essays and excerpts from his other books, plus some biographical stuff, etc., too.
Right now I have "Walden" all done (along with his "Civil Disobedience" essay), which in landscape mode takes 576 page, and in portrait 312. I'm just guessing, but by the time I add in all the other additional stuff, I could easily see that pretty much doubling the book in size/length.
Is that getting "too big" for an ebook? I do realize that the bigger an ebook is, the longer it takes to load/render. Surely there are other HUGE books that have been published in ebook format, though (James Joyce's "Ulysses", or "Moby Dick", or collections of Shakespeare's plays or whatever else)?
Thanks again, everyone!