Welcome Kevin
I babysit Robots for a crust and Home Automation for a hobby.
With OH3 being released soon I would advise to install that. In saying that it is a new peace of open source software that has not got mature documentation.
The REST api in openHAB is how the UI connects. You can do anything you like openHAB REST API | openHAB
I bought a smart kettle when it was on special (cheap) It is controlled by a ESP8266 and a TUYA MCU. I just changed the software on the ESP to TASMOTA so I can control it however I like. “Hey google turn the kettle on”
Ok do what I tell you PIC
If you want to know if it may work with tasmota look here https://templates.blakadder.com/
Openhab 2 Intergration for Kettle VScode
Openhab 3 MQTT intergration using fancy new main UI
I have a SENSIBO for my air conditioners because I bought them years ago an they just work, they are locked in to vendor. Google is my only other locked in cloud that I use for voice and voice commands. Everything in the house can be done by voice.
I made a custom widget for it in OH3
You can utilise the Google Home app to control everything even your DIY home front door lock with a pin number. But your door should unlock when you walk up to it right.
IFTTT integrations 
Just use openHAB rules.
Razberry is a no from me because I use bluetooth
Note: On the Raspberry Pi 3 you cannot use Bluetooth together with the Razberry Z-Wave module since both require a real hardware UART, but the Raspberry Pi 3 only has one UART.
Get a RPI 4 4gig and stick openHABian on it, just put it on a UPS because Zram is used.
Buy a spare sd card reader and do automated full backups.
I have one of these plugged in so if I need to restore backup I just take the sd card out of reader and put it in PI
You will encounter a problem at some stage and go looking for answers in forum at others that have had the same issues on different versions of openHAB. Read the Docs search the form but when you get stuck and post on the forum put some effort in to asking a good question with enough information for us to help.