Sip has more to do with the type of integration you do with the Callmanager or PBX system that Unity will work with rather then Failover functions. You can use SIP with Unity Failover. I would recommend using the latest if this is a new install. If not, Unity 4.x should be fine but it will not be in supportability soon so we are recommending 5.x if any.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...