System unresponsive, slow, or simply not working (parts)

Question

Hi, I'm having big troubles recently. I just updated to the latest software updates, but some of the symptoms were there before the update.
First of all, the menu bars doesn't show a lot of my previous icons. Including time, date, and pretty much everything else you have by default (Spotlight is there).
Next, plenty of my applications will simply hang (mostly applications that deals with hardware stuff):
Disk Utility (please take note, even the terminal diskutil will hang, this is important, I'll get back to it later), Image Capture (I plugged in a canon all-in-one I hadn't used for a while, one that I got with the mac) hangs totally, Finder is way too often unresponsive, *exiting a session is impossible, as well as shutting down the mac (no message, simply nothing happens)*, internet access is definetly unusable (way too long lag, too often my browser disconnects or times out note that I use Safari and Firefox).
I tried rebooting the system so it might solve thing, but shutting it down in any way won't work, even for quitting sessions, as stated above.
I then though about starting a whole new system (I was planning this because I wanted to clean up this one too), like the system on a drive, my files on another, backup on another, archives, etc; but Disk Utility hangs (no gui is seen, hangs before it loads).
I also wanted to repairs permissions and fix anything like that, but.. can't use Disk Util. (both GUI and CLI)
Source of problem I think:
Not enough disk space - although I have been using the system with a lower disk space recently, I am now a 4GB free on a 500GB which is WAY below the recommended 15% free space at all time
Fonts - Yes, I have lots of issue with fonts, so using Linotype Fontexplorer X I de-activated all the fonts not listed under "System Fonts" (otherwise I had too much at the same time) but I now see a lot of website using standard fonts with replacement fonts, this sounds bad.
Possible bad updates?
I am thinking of booting up another spare system I have (of course to prevent such problems from turning worse (everyone should have another spare system)) and then start over a whole new system.
Any ideas on how to import files and program (and settings, if possible) in a smart way?
I would appreciate any help because I am currently experiencing a lot of small problem rendering the whole thing useless, if you have any ideas or suggestions this would be really appreciated, thank you!
Edit: I can't even post this a the time of writing. The lag I have restrain me from uploading anything to anyone, and permits very low downloading. I had to save this text somewhere until it finally worked posting.
Edit: I tried adding Menu items in the Core Services folder, manually. Nothing happenned.
Edit: iTunes awfully long to load too. I dare checking any other apps.

Answer 1

First step to a cleaner system:
Make way!
OS X needs at least 15% of your startup disk to work proprely.
A lot of experts even in these forum has confirmed this, and this should be a general rule with no exception.
As my startup has 500GB, I'd need to have at least 75GB more or less (more more than less) space free.
Using GrandPerspective , I was able to find out who were the culprits using huge disk space, often without good reason. These including gigantic duplicate backup of older system (old win/unix laptop lying around), copy of DVDs (WHOLE copy, god, oh god why?) which were blottering up all the space.
Other utility of the same genre as GrandPerspective available are: Disk Inventory X (slower than GrandPerspective in my opinion) and TreeSizeMacOSX (a lil awkward to use, not so nice GUI).
These are program that will show off a graphical display of file depending on their size. Huge one are big nice easy to spot blocks, while smaller files are simply smaller square (as for GrandPerspective and Disk Inventory X). I suggest you try out both.
Once you've found the culprit, decide what would be his fate.
As for my DVDs, I am encoding them (high tech quality and encoding, yo!) using Handbrake. If you don't know about Handbrake and need to have some DVDs converted, I highly suggest you try it out at once.
+Remember to only use DVD encoding and copying for your own and personnal use.+
Results?
I have compressed a 70GB disk image to a 45GB using Disk Utility and changing the image type. Oh but since I already had the compressed one, I just made 70GB. Then I am saving at the moment 7,2GB of each DVD, as my final size is 900MB over a 8GB film.
As for my pictures, which are consuming 100GB of my disks, I am currently building (or trying to) an automator action to resize and compress all the picture I feel less confident about keeping, but that I can't get rid off (I'm sure a lot of people gets the same feeling towards picture). This will help reduce by a lot the number of high quality picture really available, as I don't really need a super RAW quality for each shots.
One last note: I recommend always have a spare workable drive, perhaps even with a partition with a system on it. In that case, if you ever need to move huge amount of data, or even your whole system, but your system won't move because of lack of space, a spare disk can come in handy in these moments.
That's pretty much it for disk space cleaning!