Bus with sub-branches is probably a good idea and will need least cables.
Do an open ring bus (both ends in the breaker cabinet, only one connected) with sub-branches then you can eg. remove a wall where your bus was going once and just connect the former unconnected end to keep everything working as before.
My home automation is wired just like you envisage.
I was in a retrofit and so I have used my existing mains wiring and supplemented each light switch with a switched live back to my distribution panel. Actually this comes from ceiling rose so no switches had to be replastered. These go onto relay(s) that are all switched by one control signal that switches between ‘automated’ and ‘traditional’. I can therefore revert the house to an absolutely normal wiring scheme should I vacate.
I actually use Schneider C-Bus (Clipsal) and am very happy with that choice but if I was in a new install now I would probably go KNX or maybe Loxone. I personally avoid any RF based devices if possible. My C-Bus is integrated with HA via MQTT.
KNX is expensive but very solid and there are many installers. The software licence (for configuration) can be expensive too. Bear in mind if you get an installer involved they will own your project file. They may well give this to you but invariably they then disown the whole project as soon as any modifications are made and charge again to rectify any errors you have introduced. It is surprisingly easy to destabilise a large KNX configuration.
There is currently a discount for HA users 
have a look at the integration documentation for a link.
You get a significant discount once you complete KNX’s eCampus online training too. Not sure if you can stack discounts? Im toying with setting up a smallish KNX install here to familiarise myself. ETS6 home should suffice.
KNX is not as prevalent in the UK as it is in EU.
There are also up to -30% or even -40% discounts (at least for Professional - not sure about Home) every once in a while (~4 times a year) on knx.org