"if i do a complete time machine backup, change the HD, can I restore directly from the time machine backup onto the newer, bigger disk?"
Do it this way:
First, get one of these devices:
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=usb+sata+dock&x=0&y=0
(some cost only about $20, and will remain useful to keep your old drive in, after it is swapped out)
Once you have the replacement drive, do this:
1. Put it into the dock and connect the dock to the Mac
2. Use Disk Utility to initialize the new drive
3. Use CarbonCopyCloner to do a "full clone" of your [old] internal drive to the new, docked drive
4. Once the clone is done, DO A TEST BOOT to be sure that it -is- in fact bootable and that it -is- an "exact clone" of your old drive. To do that, restart, and as soon as you hear the startup sound, hold down the option key and KEEP HOLDING IT DOWN. In a few moments, the Startup Manager will appear and you can select the docked drive as your boot choice.
5. If it's a good clone, the Mac will now boot from the docked [new] drive. When you get to the Finder, go to "About this Mac" and check to be sure that the docked drive is indeed the drive you are booted up from, as it will look EXACTLY like the old drive.
6. NOW, it's time to do the drive swap, because you have the cloned and tested drive all ready to go.
Once the old drive is swapped out, you can keep using it with the dock as your backup. Just use CCC to do an "incremental backup" from the new internal drive to the old internal docked drive. This is better than Time Machine because you will always have at-hand a second, fully bootable drive for emergencies. You CAN'T BOOT from a Time Machine backup...
