Not stupid.
When restoring a system from a Time Machine backup, you use the Migration Assistant. You can specify whether to restore everything (including apps) or just the accounts and shared data files.
When I'm setting up a new system, I first create an administrator account and use it to configure OS X, to install all my apps. THEN I restore just my working accounts and shared data from the Time Machine backup. That way I know that my data and settings for each account are properly installed, and I also know the OS and applications are fresh and properly installed.
An up to date system with the latest version of OS X, 4-8G RAM, and a startup hard drive large enough to contain all necessary files with 200-300G of free space makes the best base of operations for image processing. Put big photographic files ... the original raws, TIFFs, etc ... on an external drive and load them by reference into Aperture or Lightroom. Back up the system and your photographs consistently. That way everything remains safe even in the event of a problem.
G
(A piece of advice from my years of doing computer consulting with private clients: Try to let go of the notion that your computer is infinitely complicated and impossible to learn. I find this is the stumbling block that most often leads people into making a mess of their computer. Computers are complicated, but very few people need to know everything, and certainly no one learns what they need all at once. Consider them more as entertaining machines that you need to learn just enough, and maybe a little beyond, to get what you want done. And don't be afraid to explore new bits now and then, to keep the learning cells awake and happy. There are very few things, other than mass, permanent deletion of important files, that cannot be figured out and fixed when a computer goes awry—they're just glorified combinations of a television set and a calculator, after all. ;-))
