Welcome to a world of pain.
Read the notice of race and the regs, its a lot of work.
www.sailingresources.org.au/safety/specialregs/www.orcv.org.au/devonportYou might need a hull scan, stability assessment and scantlings certificate (see section 3.03) depending on the age of your yacht. If your type of yacht never been at cat 2, its hard to imagine a typical cat 5 going to cat 2 for less than $10K, could easily stretch to $40K or more. Others might have different views, but I have looked into to it a few times.
A yacht with a current cat 2 rating, with all the safety gear & systems is worth quite a bit and much easier to keep current than to start from ground zero.
Also suggest you join the ORCV and do the next beyond the bay course.
www.orcv.org.au/training/beyond-the-bay....and some of the ORCV races have a length restriction, but I think the Devonport is good for 30 footers.