Is there a log of what is been loaded at different init level? Eg. Is there a log file for modules, drivers, error messages, etc when loading init 5?

Thanks !

Not sure what you're asking. There's dmesg to show what was going on at boot. lsmod will show loaded modules. Various system logs may have info - should be in /var/log or the like. You can poke around the /proc dir to get a kernel's eye view of things. You can trace out your startup scripts (or strings of symlinks or whatever since it's Debian). This last is most relevant to what goes on at a particular runlevel. The system logs can be configured to track different bits of information in different degrees of verbosity. Check out the man pages for syslogd and klogd or whatever loggers you've got as well as all the other commands I mentioned, and the 'See also' parts of those.

Most of your logged data end up in /var/log/messages