How to prevent temporary files from growing above 2GB or less?
You are probably pertaining to the log files. The most trustworthy way to prevent log files eating the rest of your disk space is mounting your
/var/log directory on a 2GB partition. This might require repartitioning and might be harder if you have no spare unpartitioned space on disk and haven't setup LVM.
How long does it take to accumulate that 12GB worth of log files? If the answer is less than a week, then you probably have an erratic/misconfigured hardware/driver/software that constantly pushes something on your logs. You probably should start with what's causing your logs to be big.
And what is "Rotated logs" logging, only the Firewall?
Rotated logs are simply archived log files. You can safely delete them if you don't need to diagnose your system's status on the past few days.
Not sure what you meant with "only the Firewall" though.