I'm in the same boat ... just starting to set up HomeKit.
What I've found frustrating so far is a lack of clarity about so many aspects of it. I'm sure my answers are in some of the reading I haven't done yet. But HomeKit is really far from a "just works" experience Apple was traditionally known for.
1. I have a 3rd. generation AppleTV here. I keep reading conflicting information about whether or not it can serve as a HomeKit hub. (You need some device to serve as one, if you want to be able to issue HomeKit commands when you're not on your local network.) I know an iPad can serve as the hub, but I dislike that idea since I do take my iPad outside the house with me at times. The AppleTV seems the most logical, but all the recent information I see claims you need the 4th. generation model now? I'm not sure if this is because HomeKit on iOS 11 increased the requirements and back on iOS 9 or 10, the 3rd. generation AppleTV was still viable?
2. I'm irritated about my Chamberlain "MyQ" enabled garage door opener. I bought that a few years ago with the promise it would be HomeKit compatible. I had to pay extra for this wireless gateway, which allowed a MyQ app on my iPhone to communicate with it. Now, I discover they never did get that gateway to work with HomeKit, so you have to buy another bridge device for that. They had an "introductory price" on it for a little while, but that's over and now the thing is over $70. That seems to be a common story with HomeKit support. A lot of vendors promised it for their smart devices, but wound up making you buy newer versions of their gear to make it a reality. Too much of that would drive a LOT of people towards competition like Alexa or Google, since they work without that need to "re buy" things.
3. I just bought a "WeMo bridge" and am going with a combination of a few of their smart plugs and wall switches. Not sure if this is a good choice or not, but the smart plug I tried out seems to work well. I like the fact my local Best Buy stores carry these items, though. So much of this stuff has to be obtained via mail order....