As part of this, we also enabled a secondary calendar via the Multiple Calendars feature. Any gotchas to watch out for when swapping back and forth between the calendars?

do you have the first calendar for your current year which ends in the purchase period and another year that starts within new company? Usually there is purchase accounting involved and usually assets are part of it and you would need to match the balances at the top level to FA detailed level meaning likely you will have to dispose and/or revalue your assets..

do you have the first calendar for your current year which ends in the purchase period and another year that starts within new company?

Yes, though FAM doesn't seem to see periods, just dates. I tried running an asset as of the end of the stub month and it ignore that attempt since the depr schedule was slotted to go at the end of the month. I was just doing to have the team run depr as normal and then manually calc/reclass the amount that should go to the company that's ending. You think there needs to be more than that?

Are you the purchasing company or you are the company being purchased?

The latter

then see my original message. Wait until you get your purchase journals, and it will be clear then. Most of your assets are likely to be written off