My thoughts having recently done this:
1. FAM doesn't deal with this situation well or I wasn't patient enough to figure out how to deal with it. I ended up just letting it do its thing for a full month and then did a JE to fix. That said, our Fixed Assets was an inconsequential piece of our books. If that's not the case for you and someone might get upset that the depreciation on individual assets is "wrong" as of the close date, then you might have to play with it.
2. Yes multi-calendar is your friend. Set up an alternate calendar with the year and quarter ending on acquisition date. I'd keep the other calendar "normal" other than the period where you don't have a choice
3. There will be some general reporting issues you'll have to deal with ad hoc, just because NS obviously is not really set up to do this type of thing. And Jimbo is absolutely right, a year later is almost worse because you find out what you didn't account for. 🙂
4. Agree with others that most other things should be totally fine, though the restructure will make historical reporting more difficult
5. A curveball that bit us: make sure no scripting references the period names. That was some long-gone-from-my-company dev's solution to future-proof a script that would be expected to deal with uncreated periods that didn't yet have an internal ID to reference. Basically they set up the script to expect that all period names would be in the format of MMM YYYY, the NS default. Because people rarely change that, right? We did for our split month, creating two periods, one for the old company and one for the new company named MMM YYYY [old company] and MMM YYYY [new company].
Guessing there's a better way to deal with that, so you probably won't run into it, but that did stump us for a little bit.