Just to clear up the confusion about TravelPasses, they basically originate from the Sydney CBD. So for train travel, you can get on and off at any station which is between the Sydney CBD and up to and including the station that the TravelPass is bounded by. So using the Yellow TravelPass as an example, you could go from say Parramatta to Strathfield and get off there, you could go from Burwood to Town Hall and get off there, or you could go from Chatswood to North Sydney and get off there. So basically, any station that is between the boundaries on your TravelPass are the ones you can get on/off at. The colours are ranked in order, so using a Yellow TravelPass basically superseeds the Red one in that you can travel in all the stations bounded by yellow as well as red. The map is a bit confusing in that sense, so I hope this makes sense. So in other words, a Purple TravelPass superseeds all the other colours in that you can get on/off at any of the other colours (excluding the Airport line stations). Hope that makes sense now!
On a general note, most weekly train tickets are pretty much worth 3.5 return train trips (at student concession prices). So if you are travelling 3.5 or more days then you should get one. Even if you are going 3 days and just don't want to have to buy a ticket each day, then paying $2 extra (or so) for that convinience is alright.
You can't use a TravelPass on a private bus. They are only valid for the STA government buses (the blue ones) in the Sydney CBD and surrounding areas (depending on which TravelPass you have).