its not really that hard, there arent many assessments so far (they are only starting to kick in now) if you have done chemistry/bio before it would help (i didnt do bio in HSC)
theres about 60 people that started this year, by hard to get into i assume you mean the UAI, i think it dropped down to about 83 or 85 this year. In terms of jobs im not sure, but it depends whether you want to go with the police, or with a private investigator, there are a few private forensics services you could look into.
The course is only 3 years, if its not what you thought it would be, you can apply for a transfer. If you like the course but are worried that there arent many jobs (like i was) keep an open mind and remember that you dont necessarily have to stick to forensic investigation once you have the degree.
and for the last question, yes i did my HSC last year