Welcome. Search this forum for posts from jbarnes85 he has refurbished a Cav32 and before that a Northerner28 and those posts will provide excellent info. Assume he will chime in soon.
Of course not possible from your post to comment on the condition of the yacht but in short - just do it. Budget in standing rigging renewal in the next 5 years and in the meantime treat it right with corrosionx as needed. For diesel servicing suggest give Ian at humemarine.com.au a ring. Numerous other diesel mechanics around the harbour.
Slipping and antifouling - if you want to do it yourself with their preparation help Balmain Slipway and Marine Services (under new management as per April Afloat magazine page 8) is your slipway. I have slipped there in the past under previous ownership as a DIYer and had no problems - you need to make a good plan for the work flow you want to do and get a team of mates and hope for good weather.
www.balmainslipway.com.au/Else go to your local slipway wherever you are in the harbour.
If you want dive services to address the growth of the last 18months before slipping UWDS is excellent.
www.underwaterdiveservices.com/Have you got insurance covered? search this forum for insurance advice.