What’s needed to start building out a homekit

No. Though having a device such as a HomePod mini means you can maintain control while you’re away from home, and works rather better for Siri interaction. And, well, for tunes.

Set up your HomePod, HomePod mini, Apple TV, or iPad as a home hub - Apple Support

Some HomeKit devices can require their own base for interoperability with HomeKit, such as the Hue Bridge used with Phillips Hue lighting. (I’ve not used Hue. The HomeKit lighting I’ve worked with ties directly into HomeKit sans “bridge”.)

I’ll just add my input that I use my Hue lights with HomeKit (and Alexa) and they are super reliable, and then I also have my Hue dimmer switches mounted over my dumb ones, meaning that no one can break the smart connectivity. Would recommend.