IPS Setup

We manage a handful of newer Fortigate devices (v5.2-5.6) which have licenses for the Intrusion Prevention security feature, but it has never been configured. We reviewed the instructions at http://help.fortinet.com/fos50hlp/56/Content/FortiOS/fortigate-security-profiles/IPS/Enable%20IPS%20scanning.htm , but it doesn't appear to answer all of our questions.

1) Is there a "best practice" rule for adding signatures and filters?

2) Are there some that should always be enabled?

3) Is it possible (or desirable) to do a "select all" when adding these?

Thanks in advance for your time