Where's all of this SSD space coming from?

I do not really know, where the music, video and photos come from, as I never cared to look for them, but they are probably system inherent.

What is this "Other" in the storage tab? What is eating up my space? by theSeb

To find out, where you storage capacity is being used, you can use the following free applications:

• DiskInventory X
• OmniDiskSweeper
• JDisk Report
• GrandPerspective

Maybe try a combination of several, if you still can't find the "missing" capacity.

As for iPhoto and iMovie and GarageBand, they come with every new Mac for free. Only upgrades have to be paid for.

 

The photos might be all the default options for wallpapers.

The music might be all the garageband loops.

Other is probably all the system files (OSX) so that the computer actually is useable.

 

Click the Apple sign in the top left then System/Software Updates. It will check for updates then prompt you to install some including 10.8.4. Music is more of the default loops and sounds in Garageband rather than OSX sounds. No antivirus software is needed for Macs but they are encrypted and you can turn on FireVault for added security.

 

Menu Bar > > Software Update

Not really, as Windows or most Linux distributions do not come with AV software preinstalled too.

Currently there are zero viruses affecting Mac OS X in public circulation, but there are other kinds of malware existing, that can infect your Mac, but that can be avoided via employing the proper security steps without the help of any anti virus software.
To learn more about malware in Mac OS X and what steps can be taken to protect yourself, read the following F.A.Q.:

Mac Virus/Malware Info by GGJstudios​

 

Probably.

Thanks, did not know that, but then again, Windows was always more prone to malware, Mac OS X is quite quiet on that front, with some exceptions of course.

I have run Mac OS X on several Macs, even in work and network environments, without any AV software and have been quite happy with it, but I probably had some common sense due to past ignorant mistakes in that direction and Windows and its plethora of malware back then.