1) It is typically recommended to do a reinstall of your OS when you are going to a completely new motherboard. This is the cleanest process to avoid possible BSOD / Driver Issues. If this isn't really an option, I would make sure you have your OS still handy, so you can run a "repair" on the system (if need be). Also, I would boot into Safe Mode prior to installing drivers and use a program like DriveSweeper to remove all the old drivers related to your old board. Once that is completed, boot up as normal and install the motherboard drivers.
2) As for replacing the motherboard, it is pretty much like doing a new build so follow the same steps as you initially did. I would mark your case connectors with what they are before removing the old board to be on the safe side (not necessary if already clearly marked) so you have an idea how to match up with the new motherboard. Here is a good thread to review of things to watch for (or troubleshoot if need be): http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems