Hello amnd,
It seems to me that the appropriate "assistant" for you is "Home Assistant".
HA is an automation system that has integrations for a lot of IoT devices, and the latest versions is getting much easier to set up as well.
It is however an open source project, which means that it may be a challenge to get going if you have no experience with things like raspberry Pi's or Linux.
HA is also working on their own controller, but as of now people mostly run it on mini-PC's or similar.
if you're completely green on electronics and coding, perhaps Homey is a better bet.
when you have a system like this, you can connect to appliances and IoT in different ways, it all depends on how smart the devices are, and how the company that makes them integrates to other systems.
Regarding speakers, you get all kinds of wifi speaker systems, depending on where an how you want it.
Most automation controllers can be reached from outside the home through an app. This system can in practice be your alarm system if you connect motion and door/window sensors.