Home kit
I want to set up my home using home kit and get a few accessories. prior I like to better understand how these connect and whether i need to upgrade my router for example. I currently use a time capsule which is however a few years old.
Here is a good tech article.
https://www.tomsguide.com/us/apple-homekit-faq,review-4195.html
I would read it very carefully front to back, inside and outside.. until your eyes bleed.
Key aspects of home kit is how it communicates to the devices.. mostly wifi and most if not all will use 2.4ghz. Or bluetooth apparently.. which is news to me.
So what you need is excellent 2.4ghz wifi throughout your house.
You do not need to use Apple routers.. clearly the case since Apple went out of the airport business 2.5years ago. However if the TC is giving you good wifi coverage now it will be perfectly adequate. As the items multiply.. remember every single IoT device needs a separate connection. It will quickly overwhelm a single router. Hence using mesh makes huge sense. So at some point in the future when you do replace the TC go mesh.
Remember too once you make a commitment .. you are stuck.. divorce is expensive..
Alexa, Google Assistant and HomeKit are all incompatible (by design one would think). Home automation is next big thing.. but all bleeding edge entry is going to cause blood loss.
Have fun.