Well, it depends on what exactly you want. Smarthome is for now just a term for glossy magazines. Everything can hide behind it.
KNX basically only exists wired. The radio solutions in KNX are exorbitantly expensive and are really only used when there is absolutely no possibility to lay a cable.
Depending on what, how, why and for what you want it, you can already realize KNX with 5000, but then it will really only be an isolated solution like e.g. only roller shutters or only lights and sockets.
With 10000 you can do a little more, but you don’t really get into the area where it starts to be fun.
Because KNX requires the necessary infrastructure, i.e. more cables, larger cabinets, etc. The control cabinet alone, fully wired and with a basic KNX peripheral (power supply + interface), can easily swallow 2-3 thousand.
For homeway I would not necessarily spend extra money now. Just lay satellite cable and CAT7 in every room and that’s it.