Q: Home Kit is for Just Voice Commands?

Yes, HomeKit is just a framework that allows other apps to communicate with each other and the services built into iOS. There is no Apple app that puts it all together.

Let Apple know what you think of that here...

http://www.apple.com/feedback/

No, HomeKit is NOT mainly for Siri use! Siri voice control is just one of the benefits of using HomeKit compatible devices.

HomeKit is a developer framework that home accessory manufacturers of can use to create home automation products that are not only easy to use but extremely secure. These include lights, light switches, room sensors, thermostats, smoke and carbon monoxide detectors, door locks and garage door openers to name a few. HomeKit, with the addition of an Apple TV (optional), also makes it easy to control your devices remotely away from home and that also includes the ability to use features like geofencing to control devices as you arrive and leave your home.

Apple developed the framework so that developers could quickly write apps to not only control the manufacturers' own devices but also all other devices compatible with HomeKit. Unfortunately only one developer of home automation products has built their app to control all other HomeKit devices and that is Elgato Eve. There is also an independent developer, Matthias Hochgatterer, who developed an app called, Home - Smart Home Automation, that will also control all HomeKit compatible devices.

I'm sorry you are wrong. The Elgato Eve app does control all current HomeKit enabled devices.

Note: You must install and set up a HomeKit compatible device before it can be seen and controlled by other apps.

Nest products are not HomeKit compatible.

The Honeywell Lyric Wi-Fi thermostat can be controlled with the Elgato Eve app (as well as the Home app.) It is the only HomeKit compatible thermostat the Honeywell makes.

http://yourhome.honeywell.com/lyric

Also, the Home - Smart Home Automation app developed by Matthias Hochgatterer can control all HomeKit compatible devices.

Glad I could help to clear up any concerns you may have. I will happily answer any questions you have based on my own research and experience with HomeKit enabled devices.

Now on to your questions.

1. Since I don't have the Honeywell Lyric thermostat I can't tell you exactly what is involved with that particular device and app but set up is very easy with HomeKit devices. Every HomeKit device has a special code on them. During the installation process you will use the code to add the device to your iOS device. The code can be entered by hand or you can use the iOS device camera to scan the code in for you. HomeKit does not work on Mac OS X computers so a computer is not necessary.

More info here: Use HomeKit-enabled accessories with your iPhone, iPad, and iPod touch - Apple Support

2. There are five (5) apps featured on that page. It would be easier to give the web site address for each manufacturer so you can learn about their HomeKit devices yourself.

NOTE: Some of the apps, like the Lutron Caséta app, will also control non-HomeKit devices. This does not make those devices HomeKit compatible. They will not integrate into the HomeKit ecosystem and may not benefit from all HomeKit has to offer.

iDevices: http://idevicesinc.com/

Lutron Caséta (I currently have this): http://www.casetawireless.com/

ecobee3: https://www.ecobee.com/

Elgato Eve: https://www.elgato.com/en/eve

iHome: https://www.ihomeaudio.com/experience/smarthome/

3. Apple has a constantly updated list of HomeKit compatible devices here: Find accessories that work with Apple HomeKit - Apple Support

Some additional info:

These developer videos will give you an idea of Apple's vision for HomeKit.

Introducing HomeKit

What's New in HomeKit New

You can also get a lot of information by going to https://www.youtube.com/ and searching the name of the devices you are interested in. There are many users posting reviews of HomeKit enabled devices.

Here is one that shows many HomeKit devices used in a home. https://www.youtube.com/watch?v=-2kc6M1fJPE

That video highlights the use of Siri but HomeKit also allows the use of remote access away from the home and automatic triggers based on time-of-day, sunrise/sunset, geofencing to name a few. You can also set up conditional based triggers, for example: If the Smoke/Fire alarm goes off, that can cause all the lights in the home to turn on and the doors to unlock.

You might be interested in checking out this new app. Called Hesperus and it's free.

Link to review by iMore: http://9to5mac.com/2016/04/22/hesperus-homekit-iphone-app/