1. disk defrag is not needed, in fact there isn't an official tool to do it
2. disk cleanup: as mentioned, long running services usually log under /var/log and have a logrotate entry. You may want to check those are set, and keep an eye on them for a while until you get a sense of the correct settings for each one. Depends how busy your system is and how much disk space you have
3. service restarts; should be unnecessary
4. I'd recommend checking the contents of /var/log/messages, audit, secure regularly, just to keep an eye on things. As mentioned, logwatch can automate this somewhat.