There's some good info here already but, from reading the original post, I'm not convinced you understand the core purpose of Loxone. Apologies if you do and you just want some help with specifics (audio/voice/wifi) but here's a very brief overview to hopefully help you understand Loxone better.
Loxone is primarily a control and automation system. You can connect almost anything that can be controlled to it such as lighting, heating, security, blinds, garage doors, gates, energy (solar, batteries) and much more. You can, of course, connect audio and video components and use voice control (using a 3rd party add on). Loxone also monitors sensors as part of the control and automation piece, such as temperature, light, presence, open/closed sensors, weather sensors, and much more.
Loxone produces its own range of proprietary components that are easily installed and configured/integrated. You can also interface with open standards such as DMX, DALI, IP control, 1-wire, RS232, and much more. In general, the Loxone proprietary gear is more expensive than using open standards.
Whatever you integrate into Loxone can be linked up to interact and trigger each other. Temperature sensors don't just control the heating. They could, for example, be used to trigger lighting when the temperature goes above a certain value. And motion/presence sensors don't just trigger lighting, you could have them trigger the heating and audio (because they know you're in a room, or not).
Loxone is NOT primarily a multi-room audio/video system, there are better stand-alone systems for that type of application. But if you are integrating lighting, heating, sensors, and other control and automation then it's perfectly possible and probably a good option to integrate your AV into it too. Better stand-alone multi-room AV systems can be integrated into Loxone if you want to.
Loxone does NOT replace or do anything with your wifi setup, it does, however, connect to your local network to communicate internally and externally. BTW if you're doing a new build, remember that the quality of reception of wifi in your current house might not equal the quality in you new house due to different sizes, build materials, layouts etc.
If you have never experienced a full Loxone setup before then get in touch with Loxone (UK) and they should be able to give you a tour of their show home in Berkshire which will give you a much better idea of what Loxone does.
Finally, as previously suggested, if I'm right about your level of understanding then you need to find yourself a good partner, and as someone else noted, don't just roll with your electrician or builder. Find someone who understands things to a deeper level such as IP networking, open standards, AV. Really grill them about their technical ability, especially logic and programming. It's all very well being able to install a motion sensor and push a few wires into a terminal but most of the value you derive from a control/automation system is in the programming of it, not the installation of the components.
Maybe, if you disclose your approximate location (country/area) then perhaps people can recommend local partners.