I have an update about the content sync. It appears that Wolf Hengevoss's video demo (which is the only documentation I've found on this topic) assumes that you are using SLD's on both ends of the sync that are 7.1 or higher, which won't be the case when migrating from Solution Manager's local SLD (it's a 7.02 SLD at highest). So, the unidirectional sync works just fine -- it took about an hour for mine, and everything came across just fine -- but there is no bidirectional sync. This morning I removed the unidirectional sync connection with the intent of creating a new bidirectional sync, and I found that it would not do it; it always reverts back to unidirectional. I assume this is because the source SLD, being on v7.02, isn't capable of receiving synchronized content, only of sending it. So now I'm stuck repeating the unidirectional full sync. I had hoped it would recognize that all the data already existed on the target and quickly go to incremental mode, but that didn't happen.
So this means step 1 of the 2nd part of my outline above is not relevant here. It also means that we will definitely need to point the LMDB to the new SLD before pointing any of the data suppliers to it, otherwise there is a potential for missed data updates.
UPDATE: To be fair, Wolf actually mentions in his written intro to the demo that his scenario is two SLDs both on 7.1, and that 7.0 sp12 and higher SLDs can be a source for unidirectional. I guess I just didn't read that carefully enough beforehand.