The facilities at the Blue Mountains were ideal, pristine, and well set up for children. You will be fine either way. There were some strollers there but they were struggling. Sling will work nicely. There is a lot of walking so I would prepare an appropriate ergonomic backpack style diaper bag.
My kids have always been happier outdoors -- rain or shine -- so I see no reason why these adventures would be crazy. Baby over 6 months so you can use sunscreen and bug spray if needed. Lots of quiet areas to sit down and feed the baby too.
Downside is the baby won't appreciate it!