Porting Espruino on STM32F415RG : questions on board file options

Hello,

I am writing an application on Pico but I use many libraries and I lack room in the Pico flash. Since the STM32F415RG is quite ideal for my application, I try to rebuild Espruino for this micro-controller.
I have managed to recompile and flash the firmware. Of course, it doesn't work ;-)
It seems fairly normal for a first attempt...
Many topics are unclear to me. So I have some questions:

• In the Espruino board file I noticed 'bootloader' : 1, on some boards this option is present on some others it isn't. I don't understand what it means exactly. Any clue ?
  
• What does mean " 'speed' : 84" in the chip section ?
  
• In the 'saved_code' section, I understand that it defines how the code once temporarily imported toRAM it is then copied to the flash; Is that correct ?
  
• If above is right, the question is to copy code in pages which in case of STM32F415RG are not uniform (some 16k, 64k, 128 k). Could you advice me on the best way to use the flash pages structure ?
  Thanks a lot.
  Regards
  GeekBot