Welcome to the community! It seems like you've been doing some reading and have some good ideas. The folks here are very helpful. I hope you have fun as you go through your home automation journey.
As you've probably seen, some topics have a variety of answers and your situation may be different than other people, leading you to different results. Costs can also be a trade-off to consider. For example, you seem to be focused more on security than I am. I'm more into controlling lights (replacing existing wall switches) and automating things like watching TV. You can see some comments I made in another post to someone coming from Smartthings (Hubitat right for me?) and they may give you some ideas. Since then I got a MyQ garage door opener with a Samsung multipurpose sensor (as you said, that provides status back to Hubitat). It's a little iffy since the API has sometimes broken the integration but the current app/driver seem to work well and for $30 on Amazon (US), it seemed like a reasonable start and it's worked well for me. If you're in the US, Samsung devices are also on sale.
I've mostly used Zooz equipment (Z-Wave) and have been happy with the price and support from them. They're also having a great sale going on. I've also added some Zigbee Samsung water sensors and Iris motion sensors and plugs (from Ebay, as @billmeek replied). As others have mentioned, ensuring your devices are connecting reliably is important and that can influence your equipment and setup.
The standard applications are a good foundation. As you spend more time on here, you'll also get ideas of what other community applications and drivers you want to add. Depending on your background, it may take a little getting used to but there are some outstanding resources to extend your system.
Finally, the search function on the board works really well. I typically can find answers to my questions or other tips and insights by seeing what's already been posted. If you don't see what you're looking for though, don't hesitate to ask.
