I suggested the PIC16F877A simply because I have some experience with it dating back to the Junun Minisumo Mark III robot. I believe it actually used the PIC16F877. This was pretty interesting stuff, 20 years ago.
At the end of the day, I don't recommend ANY of the mid-range PICs. The hardware is too limiting, C compilers have to generate a lot of extra code for paging and banking and the lack of a stack pointer is really limiting.
Personally, I would skip the mid-range PIC experience entirely. But it's hard to argue when the proposed project is so simple. The thing is, STM32F devices are all over the place and they include a programmer/debugger. I'm more of a printf() kind of programmer but having a hardware debugger has to be useful to newcomers.
The most fun micro I play with is the PSOC 6. At the moment I can't convince myself that the 4.4 version of the software works with any of the demos but 4.2 does. I really like the PSOC 6 101 video series.
If I wanted something simple, I would use the DIP version of the Arduino, get the code working and then put the pre-programmed chip in my project board. The ATmega328P is a pretty decent chip and requires little around the outside to get it to work.
I really can't get into the idea of backing up to the mid-range PICs. In comparison to something like Arduino, they are truly grim.
The ATmega328P chip, as used in the Arduino, is $2.52 at DigiKey but I would start with the kit I linked above. Learn some stuff and then deal with the proposed project.
https://www.digikey.com/en/products/detail/microchip-technology/ATMEGA328P-PU/1914589The 16F877A (40 pin DIP) is a little over $6 at DigiKey and the 16F84A is also around $6.
For developing on the DIP chip, I would use the genuine Ardino Uno board:
https://www.amazon.com/Arduino-A000066-ARDUINO-UNO-R3/dp/B008GRTSV6