Help with backup of Mountain Lion & upgrade to Mavericks

Question

I am contemplating an upgrade to Mavericks from Mountain Lion 10.8.5 on my iMac i5 with a 1TB HD (500 GB available) and 8GB memory.
Before doing so, I would like to make sure I can revert if necessary and thinking of possibly using Carbon Copy Cloner to clone my HD onto a Lacie 3TB external HD. 
Can someone make suggestions about preparing the 3TB HD?  Should I use the 3TB HD strictly for CCC?  Or is it of sufficient size to partition the drive to share between CCC and Time Machine?  (Partition size suggestions would be helpful if that's a recommended way to go).
I have never used CCC and have not yet purchased it, so if there's any other suggestions for someone not too computer savvy, they would be appreciated.  I am not currently using Time Machine, but wouldn't mind the extra safety. 
Awhile back I read some unhappy posts on the new Pages & Numbers programs, so I would also like to keep my current Pages & Numbers versions for now.
Thank you.
Barbara

Answer 1

You must first create a new partition on the LaCie. The partition should be a few GBs larger than the total amount of space used on your internal drive.
To resize the drive do the following:
1. Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
After the main menu appears select Disk Utility and click on the Continue button. Select the hard drive's main entry then click on the Partition tab in the DU main window.
2. You should see the graphical sizing window showing the existing partitions. A portion may appear as a blue rectangle representing the used space on a partition.
3. In the lower right corner of the sizing rectangle for each partition is a resizing gadget. Select it with the mouse and move the bottom of the rectangle upwards until you have reduced the existing partition enough to create the desired new volume's size. The space below the resized partition will appear gray. Click on the Apply button and wait until the process has completed.  (Note: You can only make a partition smaller in order to create new free space.)
4. Click on the [+] button below the sizing window to add a new partition in the gray space you freed up. Give the new volume a name, if you wish, then click on the Apply button. Wait until the process has completed.
You should now have a new volume on the drive.
You can now clone your system to the new partition:
Clone Mavericks, Lion/Mountain Lion using Restore Option of Disk Utility
     1. Select the destination volume from the left side list.
     2. Click on the Restore tab in the DU main window.
     3. Select the destination volume from the left side list and drag it
         to the Destination entry field.
     4. Select the source volume from the left side list and drag it to
         the Source entry field.
     5. Double-check you got it right, then click on the Restore button.
Destination means the new partition on the LaCie backup drive. Source means the internal startup drive.