I use these throughout my house:
https://www.amazon.com/gp/product/B0718T232Z/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I use this board both with a simple USB outlet, as well as higher amperage power supplies. Works well!
1) Yes, you have restrictions due to hardware limitations. 2) Not fundamentally different, just extra requirements to keep in mind. Interaction with interrupts, interfacing to hardware, portability to different processors/development environments for example. 3) Pick up a cheap development board and write a "Hello World" project from scratch. Add a resistor and LED to your project and blink it. For example using: https://www.amazon.com/HiLetgo-ESP-WROOM-32-Development-Microcontroller-Integrated/dp/B0718T232Z/ https://www.amazon.com/REXQualis-Electronics-tie-Points-Breadboard-Potentiometer/dp/B073ZC68QG/
4) I think familiarization with the RTOS and possible cloud connectivity options (such as AWS IoT), or maybe a few serial protocols, or a micro web server would be of at least as much benefit as becoming uber aware of one microprocessor specifics.
5) The Saleae Logic 8 is a nice entry level logic analyzer - useful for watching logic signals. You can get a cheapy multimeter like: https://www.amazon.com/AstroAI-Digital-Multimeter-Voltage-Tester/dp/B01ISAMUA6/ while saving up for a nice Fluke.
Beacons are just a small portion of BLE, and honestly, not the meat and potatoes portion. You can download nRF Connect by Nordic Semi on a second phone and mock BLE device interfaces. But a cheap hardware solution that is pretty easy to work with is the ESP32 based boards, this one works very well:
If you add a breadboard, a 5V/3.3V power supply board, and some buttons and wires you can make something that you can interact with to trigger events that are notified back to the phone. It can all be done in Arduino IDE using C++, but for simple stuff it is pretty easy to hack things together. This kit would give you everything else you need to make some interesting test devices with the ESP32.
If you choose to go this route, feel free to reach out if you need any tips or pointers, I can even throw together a sample program for the ESP32 if you want.
Edit: Also, if you want to mess with Beacons, a simple solution if you have a second phone is the app Beacon Simulator by Vincent Hiribarren. There may be other ones that work well, but I have personally used that one and it hasn't given me any issues.