So: looks as though the Blogger Migration tool did the job fine, with one major hiccup - a hiccup that I knew going in was likely to happen. The search function no longer works. Something similar happened with Noah's blog, which I'd moved from FTP to Blogspot hosting a few weeks back. For him, merely an inconvenience, since he'd only posted about ten entries. For me, something more of a web-tragedy, since even with the much-reduced frequency of the last few months, this particular entry is Rambler number 727. Having 700+ entries with no way to search for content is depressing, and I sure hope there's some way to fix it.
Beyond that, everything else looks like it worked fine. All the comments came over fine - my other big fear was losing them. So once I get the indexing/search function back up and running, I'll pick a new skin for the Rambler and call it a success.