Advice sought on upping 10.4.11 to Snow Kitty

I may at some point want to update this iMac's original 10.4.11 to the current OS version, Snow Kitty is it?

Been running this iMac, smooth sailing, two years or so I guess. A bit nervous about updating ... must I back up all files and take other such steps, or just run the update disks when they arrive and have a coffee while all goes perfectly and nothing is lost or does not work? I would USB stick backup if I do that.

I use several open source apps, including the essential Gimp.

Have had no good reason to update until now, but a certain .. uh .. startup company has just introduced its Mac browser, and also one other software has a new version I would like to have which requires 10.5. I am not an updater by habit or inclination, rather -- a minimalist.

I understand, of course, that I must pay high dollar for what came after 10.4.11, before I can install the almost free Snow version.

I also would hesitate if I thought the later version took too much disk space or impacted memory heavily. But seems I have heard it is actually lighter, not heavier.

Thanks for clearing my fog of ignorance.

You don't "have to" back up before installing, you can do an archive and install.....
However, in saying that, if anything goes wrong, which is possible, do you you really want to take that risk?
I prefer to do a clean install, and then restore from my backup whenever updating my OS X!
As long as you meet the minimum specs, you are right to go, and yes, it is lighter.
# Mac computer with an Intel processor
# 1GB of memory
# 5GB of available disk space
# DVD drive for installation

I hope I have answered your question

Thanks for the help. I guess Apple will tell me when I phone to make a purchase, what I need to install. Something at 10.5 before the Snow Leopard I suppose.

Here's an example of something I would be concerned about: I just bought Airport Express to relay music to our stereo in another room. Working fine now. So if I try to install my way up to Snow Leopard, does nothing change in regard to Airport and related things, or must I start all over on the network setup?

Your settings will be saved in your backup, which you will have after installation when you restore from backup.
The safest way to go is to make a clone of your system using Carbon Copy Cloner - Home or SuperDuper! , that way, if for any reason you are not happy, you can revert back to your smooth sailing setup, and you have a bootable copy!