If you were building a smart home from scratch, what would you do?

[snow ocean]

I've been running HA for a while in my current house with Hue lights and various ad-hoc things that I have added to the sytem over the years. Now I am rennovating our new house and I have a clean-slate opportunity to "do it right" from the start. The electricians that are doing the house are trying to push a Loxone system on me, but I have no idea how well this will integrate with HA or how open/rich the APIs on it are. There are SO many questions I feel totally unqualified to answer:

smart bulbs (e.g. Hue) and dumb "always-on" lighting circuit, or dumb bulbs and smart lighting circuits?
What sensors (what types and what models) should I sprinkle throughout my home?
Similarly, what switches and control surfaces should I have throughout the house? (My current home has loads of old-fashioned light switches that I have taped-over to stop people turning off the Hue lights... let's not do that again!)
What are the advantages and disadvantages of going with a branded system like Loxone vs an ad-hoc mix of different sensors/actuators/etc throughout the house?
If a branded system, is Loxone good, or what should I get instead?

There is also some time pressure here: the electricians are pushing me for a quick answer because we need to move in quite soon.

Any and all advice would be really appreciated!

[worthy kelp]

Dumb bulbs and smart switches are my recommendation for 99% of situations you just want lighting, not only are you covered in the event your zigbee network falls over but it's significantly cheaper. Obviously if you want colour control then you need to go with smart bulbs, but I've never felt the need for that

When it comes to sensors and devices I recommend

1. Temperature sensors and smart trvs on radiators/actuators on underfloor heating.
2. Presence sensors (mmwave) to do things like detect you're in bed and turn lights off (rather than trying to infer it from time of day, phone charging state etc)
3. I kept lightswitches everywhere but some of the smart interfaces are really neat and am looking at installing those soonish. At the very least, those that have both a local switch and a zigbee button are very interesting to me for room control
4. Energy monitoring - ct clamps at the fuse board is nice, but talking to your meter should be the minimum you try for
5. Water/gas meter - just talk to the meters and monitor for constant low flow that can indicate leaks

[worthy kelp]

As for loxone vs home assistant and a diy solution - I think most here are going to be more than a little biased towards home assistant.
I've just had a poke through the loxone website and their hardware seems incredibly expensive - their wireless trv is £100 vs a sonoff one in the £20 range, or even if you went with something like hive you'd be looking at £50. Their estimate for the standard smart house hardware is like £4k + installation and setup whereas I don't think I've broken £1k with diy
As for reliability, it depends - it could be better but if the company goes bust you're kind of screwed for support
The interoperability of branded systems is generally poor - they want you to use their speakers, not the sonos ones you already have, same with new sensors they don't support (e.g they don't have any mmwave sensors)
The advantage of loxone is that the base "all wired" solution is very robust, so good for things like security systems and if you want to go fully smart lighting etc because it removes the risk of vulnerability if the network goes down for whatever reason.
There does seem to be some level of connection that loxone allows which can let ha bring in zigbee devices or data from other integrations, but honestly it seems like a bit of a faff

[snow ocean]

Thanks for the detailed reply. That aligns with what I suspected -- I'm worried about paying a high-end price to be locked into a system that just isn't as good as other stuff (e.g. no mmWave).

But if I don't go with Loxone, I'm going to need to tell the electricians exactly what I DO need them to do: e.g. what, if any, light switches to put it, what wiring I need for the presence sensors I'll put in myself, etc. It's a shame this stuff isn't standardised so I can just tell them, "put a socket for a presence sensor here and here..." and then I can put in whatever presence sensors I want later.

[marble topaz]

10 years in, I'm really happy with having KNX for the basics, and the smarts in a computer on top. This is a fully wired system and no distributed components. This is manufacturer independent, in case I need to replace something.
I had to pay a little extra for the contractor to install more wires, I did the cabinets myself and they checked and connected them. It is a steep entry and whole other world to learn though.

Every indiviudal outlet, window contact, heating valve, motor for blinds and light outlet has a dedicated wire to the cabinet. No junction boxes anywhere. Speaker wires from the ceiling to the cabinet, many ethernet outlets (even good for getting audio from the living room to the amplifiers!)
For the room sensors, they are on a KNX bus, with every room having a presence/motion sensor and a programmable switch near the door.

The basics "turn on the light when presence and dark" or "button to shut the blinds" or "heating valve adjusted to room temperature" are done with KNX. No computer to fail.
The advanced stuff "when do I need shade" and "timer based lights" are done elsewhere, soon to be migrated to HA.

For the lights, I went with 24V LED spots in the ceiling and regular 230V outlets.
Not every wire is connected to a dedicated actuator in the cabinet, some are grouped and some are permanently powered. The big mess of wires connects to about 200 multi-level Din mounted terminal blocks "Mehrstock-Reihenklemmen".
I mostly went with MDT actuators, but any from the 100 other manufacturers will do.