I have 2 suggestions: I don't *ever* want to change domains again!
You will have a traffic drop, although how long for is undetermined - make sure you budget for at least several months down time.
1. if you must do this move, do it bit by bit. Split the move across 6 months. Then just as you are losing the revenue from the final pages to move, the first pages will probably come up.
2. Don't do it. Write new content for the .com site and start over. Link strongly from the old site, where appropriate, and you may want to move *some* of the content, but leave the old site in place, with country specific content.
I have 2 suggestions:
I don't *ever* want to change domains again!