A few people there have chickens, Moth does, and Frank the guy that runs the internet cafe have them. As for the tanks, yeah you will need to make a ladder that will get over them, I lived in one for a couple weeks and climbing it with a rope carrying gear gets old quick, I broke a 16lb sledge hammer trying to crack the cement on the bottom to build a tunnel out, as I wanted to live in one too, also heard another guy broke a sledge trying to get in the side of it, they were built like bunkers thick cement and a lot of rebar. Also it is extremely windy inside, more so then even outside, you can't even whisper w/o it making loud echos.
I was thinking of bringing a saw that can cut cement and rebar next time I come out there, and like someone already said just don't damage the artwork on it. Some people that were only there for a week decided they would paint over the guard post on the way into the slabs, and a lot of people got really mad. They probably just wanted to take pictures to show their friends that they had left there imprint on slab city.
And yes there are a lot of meth heads that will creep around your camp at 3 in the morning and try to steal stuff. Which is why most there have dogs.
As for farming, it is the desert, you would need to bring in decent soild, all that is there is sand and clay, you would also need a ton of water, the only way I could imagine it working is if you had a truck with a large water tank on it and a pump to pump water from the canal. There is a guy or two that have built wells out in one of the washes, I dug about 10 feet down in the sand and the soil was wet in one of the washes, supposedly during a recent earthquake a crack in the cement in the canal was made and some water leaks out into the wash behind edge road. The canal water is drinkable, supposedly ice melt, I drank it most of the time I was there unfiltered.