Ask HN: Moving to the USA with a chronic health condition

I am an Australian university student studying Software Engineering. I was scheduled be over in the USA completing my final semester on exchange right now, however 6 months ago I fell quite sick, and after 3 horrible months I was diagnosed with Crohns Disease. The good news is that with proper treatment prospects are good and life should return to normal. The bad news is that most people diagnosed are stuck with it for life, and some of the treatments can be expensive (mid $X,000 per month) if the government / insurance doesn't help out.

When I am done with uni I want to move to the USA on an E3 visa (basically H1B for Australians) to take advantage of the work opportunities and satisfy my sense of adventure. If I were to do so, assuming I were to work for a large employer (e.g. Google / FB):

1. Am I correct in assuming health insurance is provided by my employer? 2. Am I at a disadvantage already having a potentially expensive chronic condition? 3. What happens if I move jobs / become a freelancer / join or start a startup?

Apologies if these are straightforward questions, however from an outsiders perspective trying to use Google to find the answers has left me even more confused. I figure that there must be many people on HN who have been through this themselves.

As much as I want to move to the USA, being shackled by health insurance makes me reconsider given I don't have any of these problems in Australia. I am currently struggling to differentiate between the truth and the horror stories of the USA's health system