Ducted Air-Conditioning - Condenser in Roof?

We're about to renovate our 1930s top-floor apartment in Sydney (approx 80M^3) and want to install reverse cycle air-conditioning. The unit runs along the East half of the block with a part-enclosed balcony on the North and and open balcony on the South - so it's hot in summer (despite the breeze) and cool in winter.

We have access to the pitched roof void above the unit (3M high in the centre). As part of the renovation, we plan to renew all the windows, install insulation in the ceiling and the damaged terracotta roof tiles & sarking are also to be replaced by the body corporate.

We have been quoted $8.9K for a Mitsubishi Heavy Industries multi-split system (SCM60ZG-S - 7.5kW Cool/7.6kW Heat) connected to two indoor ducted systems: One with 6kW capacity (SRRM60ZF) for Kitchen/Living/Dining rooms and one 3.5kW (SRRM35ZG) for the bedroom.

The suggestion is to locate the condenser in the roof void above the kitchen and duct it to the existing vents in the gable end. The diffusers would be installed at the top of a false wall in the living room and at the top of new wardrobes, new kitchen units and a false ceiling for the new toilet will allow for the ducting to the diffuser for the dining room (see plan attached).

Questions
- I have heard that installing a condenser in the roof space is very likely to produce heat build-up problems - The alternative is to locate the condenser on the back balcony and the refrigeration pipes (5M) into the attic space through the wall - would this be a better solution?
- Is there too much/too little capacity in the unit specified?
- Should we have more than 2 zones?
- Should we go for a fully ducted system instead?
- Is the price reasonable?


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