Ian,
You are correct. TYIA or sometimes simply TYA is 'Thank You in Advance.'

HOA => Home Owners' Association This is the governing body for a condo association or covenant controlled community.
Here in the States most neighborhood developments and many condominium complexes (apartment buildings, but owner occupied) have these associations to control the populous and provide varying levels of maintenance. Think of it as a quasi-government slightly below village. I'm not sure if you have those, or what you call them if you do, Down Under.

In the case of Crystal Lakes we have about 1600 lots varying from 0.5acre (0.2 hectare) to 30acre (12 hectare) on 4800 acres (7.5 square miles, or ~1900 hectares) with 85 miles (136km) of private, dirt roads, several structures, and 6 dams to maintain. I was part of the road crew, the paint crew, and made sure the outhouses (12 of them) were sweet smelling once a week. About half of those lots have homes or cabins on them, and about half of the homes are occupied year round. For most of us it's a weekend or summer time retreat.