You can camp just about anywhere just so long as it's not within the Warragamba exclusion zone. It's always good to check with NPWS.
As for the water board land, I think you will find that you can wonder around and camp as most of my family members and rellies have done over the years. Get in touch with the Water Board and ask the question and if you do your homework properly you might be able to catch a ride down to the farm. Mind you, I'd rather catch a ride back.
I've never bothered to camp there myself because my parents lived along Tablelands Road and had a comfy spare room and bed instead.
You can fish Kedumba which runs behind the farm and starts at a junction of the water from Leura Falls and Wentworth Falls. There is also the chance of getting a trout at the base of Wenty Falls, which my brother has done in the past and is accessable (I'm pretty sure) via the "Giant Stair Case".
From memory, the water from Wentworth Falls lake runs over the falls.
You can access the farm via the main gate which is down near QV but you aren't allowed to drive down. It's pushbike or one foot in front of the other.
There are different stories doing the rounds as to what the water board are going to do with the old farm. One was to raise Warragamba and flood Kedumba but I believe it is now going to be given back to the "public" and regenerated. The land is no good for flooding because of one last remaining privately owned piece of land that the owners won't sell.
Kedumba was originally bought from Cleary Bros by the water board after Cleary's wanted to subdivide the land through Wollondilly council. When the Water Board found out it was a case of "no way we will buy it off you".
Anyway, good luck with your ventures and if anything, just check with the local authorities etc for more info.
And you don't get down there to trout, at least get down in to some of the closer valleys and get yourself a feed of freshwater yabbies. They make a good feed.
PS, I hope everything I've written is right, I'm only going off what I can remember from my past knowledge and experiences.
It's a great part of the world to explore so get out there and give it a go.
cheers
Hooky