Thanks! I knew absolutely nothing about IoT and hardware before this, but quickly realized how big and welcoming the community is. This made things very motivating and enjoyable to get started (but still quite overwhelming!). I personally started by diving into the Arduino ecosystem and the world of micro controllers, particularly the esp8266 and esp32. It's all open-sourced and there are tones of tutorials to help you get started. The most challenging part for me so far has been to go from a "DIY prototype" for personal use to a "certified, safe commercial product". It's been a LOT more challenging than I thought, and took way longer to get there. But very fun to say the least.

After you get the "certified" product up and running maybe look at selling it as a kit for the DIYer.

My favourite website is Adafruit! They have stuff to buy, lots of learning resources and CircuitPython (a MicroPython fork with lots of libraries).