1. The onboard GPU can be disabled in the bios.
2. If the old drive is IDE you may want to replace it with a SATA drive, unless the new motherboard has an IDE connection. You can simply move the drive to the new system. During the install of your OS, you will be given a chance to partition the drive. Delete all partitions and create a new one for the OS. Be sure to back up any data before this step.
3. You can use the drivers on the motherboard CD, but I always like to download the newest ones before hand.
4. Cabling is usually easiest during the build instead of afterwards, especially if you have cables you need to run behind the motherboard.
5. Seven fans is ok as long as you don't exceed the maximum rating of the PSU.