Greetings from Melbourne!
I've got three Indigo systems operating across separate properties, and I've responded based on my experiences to date. Two systems were retro-fits, and one a new build. My approach has been sensible and pragmatic - do you really need to automate/have remote control of ALL devices? Will it meet the Wife-Acceptance-Factor (WAF)? Do you need to monitor energy consumption of each individual load? Etc!
You don't say if you are doing this yourself, or specifying a system for others to install and maintain.
I am using a mix of ZWave, Shelly and proprietary devices with non-cloud API's. With regard to Cat 6 cabling, go for it. In my last (new build) installation, I have run cable everywhere, but it seems little of it has been used except for PoE stuff (cameras, door intercom, etc).
My specific comments to your queries are:
a house designer suggested a technology I hadn't heard of at all (Clipsal C-Bus)
If you think ZWave and Insteon expensive, wait until you price C-Bus!! It's an older technology, requiring detailed (and in my limited experience) complex programming by a certified installer. It's also centralised, requiring all circuits to be wired back to a switchboard. My recommendation is to give it a miss! If you're looking for a "whole-house" solution you might check out KNX, but I have no experience in this system.
- Lighting (seems like all solutions are a micro controller behind a Clipsal Iconic switch?)
- Powerpoints
- Shades / Blinds
A major issue is the availability of devices certified for use in Australia. Failure to use such devices raises insurance liabilities, and potentially, on a new build, may result in issues in obtaining a Certificate of Electrical Safety (or whatever it's called in Queensland.) To this end, I have transitioned to Shelly and Fibaro devices, many of which are certified for Australian use. More recently, I have used a number of the Deta Grid Connect switches and power outlets from Bunnings that are Tuya enabled. I have flashed these to Tasmota, and using with the MQTT plugins with good success.
The obvious choice for shades and blinds is the Somfy system. I have yet to use these, but am about to embark on an new installation using these. Instead. I have elected to use the Neo motorised blinds with the "Neo Box" interface to Indigo. I initially wrote a Python script for this, but howardtp took pity on me and has written a plug-in to support this device!
- HVAC (System hasn't been selected, but it will either be a multi-room, multi-zone ducted system, or mini-splits in key rooms. If one brand's controls are better suited for HA, then there's an opportunity to make that recommendation.)
I have a mix of systems including an early a Daikin ducted reverse cycle installation. It's fitted with their SkyFi system that was so bad they discontinued it. I wrote a series of Python scripts to support this, and it's still in service. The latest install uses Daikin splits, with Broadlink RM minis issuing IR commands. Not recommended as it has no feedback as to status of each unit. Whilst the Daikin systems are great for air conditioning, they seem to be lagging in the wi-fi control area so you need to shop around!
- Security (Contact, motion sensors, smoke/fire and so-on. I think ideally, this is a separate system with API, but I'm willing to be swayed otherwise. I want to avoid battery-powered sensors, so this seems limiting)
I have always maintained that if security is important to you, it should be of good quality and totally independent of any HA system. If you wish to arm/disarm under automatic control, this should be done via hard wire contacts rather than any high level communication between systems! With regard to smoke and fire detectors, I believe that Clipsal now (or will shortly) offer wifi connected detectors, but as these are subject to regulatory requirements they also need to be treated independently of HA - unless you duplicate regulated detectors with others connected to the HA system!
- Door Locks
I'm using Lockwood/Yale Wires Digital Deadbolts, fitted with ZWave modules. These are supported in Indigo with the Lock Manager plugin. I have the devices with keys so that if anything goes wrong, you're not locked out! It hasn't happened yet, and the oldest of the four devices has been in active service for about 5 years
- Solar PV & Battery Storage
I have not yet committed to batteries, as they are yet to make economic sense in an area with a reliable grid. This may change soon if export limiting is introduced! I have three separate grid-connected PV systems:
- One 6kW system using 2*3 kW Fronius inverters with a network-connected "Smart Meter" that I "interrogate" and report on in Indigo using the Ghost XML plugin
- Two Enphase micro-inverter systems (one 3kW the other 6kW). There is an Indigo Enphase plugin that allows reporting
The reporting is presented graphically on a control page using Matplotlib plugin. I favour the Enphase micro-grid system as there's no large box on the wall and you can get reports on the performance of each individual panel (see screenshots).
For a new build, I suggest that you make space provision for inverter and battery installation, having careful regard to the relevant Australian Standards. I also query the need for "per-circuit" energy monitoring on a permanent "in-built" basis, as the global view available for the solar reports I have found to be adequate (training householders to run major appliances during peak-sun hours!) and for automating appliance operation when there's an abundance of solar power!
- Cameras (probably Security Spy unless there's a more integrated solution).
I started with an independent network video recorder (NVR), capturing snapshots using Python scripts to present on control pages. Again, if security is important, independence from the HA system is advisable. On my most recent system, I have been using Hikvision PoE cameras with inbuilt SD cards - again distribution of recordings increase the reliability should one device fail ie the recording is located on the camera, but accessible if required via the network. These cameras also have quite sophisticated motion and intrusion alarms that can be used to trigger lighting, etc on the HA system.
I'm afraid I'm unable comment on the other items your considering. However, as with security , I suggest that critical systems (eg septic!!) remain independent!
Hope that helps - happy to provide further info if required