Where to start developing BLE?

Question

Bluetooth

Good day to all!
I'm a programmer, I write mostly in Python and Javascript and a little bit in PHP, and in general I don't consider myself dumb). There has always been an interest in microcontrollers and various sensors, but unfortunately there is absolutely no free time to do this as a hobby, I didn’t want to spend money on this ... That is, I’m generally a noob in this business)
Now I have the opportunity to work in this area, since one of my friends wants to stir up a simple device that should connect via Bluetooth to the phone at least. I asked him not to turn to the Chinese for the time being, but to give me the opportunity to try.
So I have a couple of questions for the experts:

1. For example, this Dialog da14580 controller , can it be programmed, that is, can it be made to simply turn on and off the LED through the phone?
   
2. To put it bluntly, are all microcontrollers programmed in the same way, or do you need to buy something separately for each controller?
   
3. What other devices do you need to buy to program this or similar controller?
   
4. What programs need to be installed? Is it possible to program under Linux?
   

In general, I will be glad for any help. If you don’t feel like writing stupidly, then throw links to tutorials, I will read and understand.
Thanks in advance to everyone who can respond!