First time I did Mobile Odin and wifi didn't work.....Second time I used desktop Odin and it did.
How do you clear the data and system partition? Maybe it is just different wording, but have never done that.
So, what you are saying is that you can restore the data from the apps? Everything will be lost?
If you have CWM Recovery installed, you can easily go to "mounts and storage" and hit the format on the /data and the /system partition.
If you're on a stock recovery, a couple of flashes from Odin does the same thing. You know everything went well if the static boot logo of "SAMSUNG GALAXY S III" doesn't stay there for an awkwardly long time.
And for your last question, yes, if you try restoring data of your apps, they will crash.
HOWEVER, I have
NOT tried restoring with Titanium Backup yet. I used other methods. So try to give some apps a go. If the FC, then I am afraid the truth shall prevail: You cannot restore data. If you have some game .OBB files, for Asphalt 8 etc, you can find their data in the /sdcard/0/Android/obb or /sdcard/0/obb and place them back into /sdcard/Android/obb for them to start working again.