Good to see you made the switch, welcome to the light.

The Apple software updater will only show you updates that are specific to your computer and to the software that is installed on it. It reads the files in the Library/Receipts folder to determine what Apple supported software you have installed.
Indeed, some of the updates are very large, OS 10.5.2 is a whopping 343MB! Other updates are not usually as large as that though but they do lean toward the 75MB mark.

iLife is installed on all new iMacs and, unless you or the previous owner (if there was one), removed it, then it is still there.
iLife is a collection of programs, iTunes, iPhoto, iMovie, iDVD and iWeb. I think you will find you have them.

Bottom line: If the Apple software updater says you have updates to download, you can be sure that they apply to your machine.

Console messages are something that you do not normally see. The console is rather like the Event Viewer in Windows. It allows you to view just about everything that happens when you do something on your Mac.
You do not need to do anything with it.

Automator is a very powerful tool that will allow you to create scripts to carry out repetitive tasks in one easy step.
Take a look at it; it is quite safe and fairly easy to use.

Now that you have found us, feel free to ask any Mac questions you have