Just a couple of notes to be aware of:
Collett's are not all puppy dogs. Many I've dealt with, including a couple of big captive-bred 5-6ft snakes, remain very flighty and bitey after a decade. It really comes down to the individul snake, as it does for many other species, including Inland Taipans.
Additionally, the correct antivenom for Collett's is Black Snake Antivenom. I think you'll find most hospitals in Sydney probably don't carry this antivenom as the only black snake in the Sydney region is the Red-bellied Black Snake, for which Tiger Snake antivenom is used. However, Tiger snake or Polyvalent antivenom may work for Collett's, although it is not as effective.
Venomous snakes certainly behave differently to snappy pythons and a bite can potentially kill you so I would seriously consider whether or not you really want them. If you do decide to go ahead with getting one, make sure you are fully aware of the correct first aid for snake bite. You would be suprised at the number of herpers with venomous snakes, who have no idea about the correct first aid ie. how tight the bandage should be, where you should start from, what actions to take etc etc.
For info on snake venoms and first aid, take a look at the website
www.avru.org.