Nice picks for hobbies. I'd just like to say that all of that are rabbit holes with quite some span and things to learn... Tinkering with electronics, learning how to program and webservers and sysadmin stuff like networking and services deployment.
Considering the self-hosting I'd recommend to start out with an out-of-the-box solution. Like yunohost.org or DietPI or a few others. It gets you some results and is usable in the real world without studying textbooks and larning Docker and Linux for a few weeks full-time.
With programming Arduinos and microcontrollers: Have a look at projects like MicroPython and CircuitPython. You can also install the Arduino IDE and see if you like it but programming in C is a steep learning curve. Maybe less suited as a first programming language. I can recommend the ESP32 microcontrollers. They're awesome and have wifi and you can do lots of home automation projects in addition to everything an Arduino can do.
I think neither of that is low-tech. The chips and software itself are state-of-the-art technology. From my perspective you'd need to add the "low"-aspect with some context. Make them solar-powered or host a blog on those services.