Changes I did:
Have the protocols in RAM
#ifdef ESP8266
// because of timing reasons we keep that in memory on esp8266
static const RCSwitch::Protocol proto[] = {
#else
static const RCSwitch::Protocol PROGMEM proto[] = {
#endif

Changes to receiveProtocol (called by ISR)
#ifdef ESP8266
bool ICACHE_RAM_ATTR RCSwitch::receiveProtocol(const int p, unsigned int changeCount) {
#else
bool RCSwitch::receiveProtocol(const int p, unsigned int changeCount) {
#endif

Source: https://github.com/sui77/rc-switch/issues/46

on Issue 1: Arduino is configured with both cores already when built, so nothing else is required.
on Issue 2: Could you try to lower the flashing speed? You seem to have selected 921600 and I have seen that to fail on my mac too. Try with 115200 as a safe net and report how that goes. To note, I have had success with many baud rates with FTDI chips, but not the same with others. Silabs seems to be better than WCH, but not quite as good as FTDI.

Source: https://github.com/espressif/arduino-esp32/issues/333

Source: 10pcs New HT7333-A HT 7333-A TO-92 Low Power Consumption LDO | eBay

Source: Make Your Own Fritzing Parts – learn.sparkfun.com

http://danyk.cz/avr_aku_en.html

If you create an Arduino project with the principal .INO file and a few other .INO files in the same folder the Arduino IDE will load the principal file first and then load the others in alphabetical order. A global variable will be visible in all files loaded after the file in which it is declared but not in files loaded before. So the best place for global variables is in the principal file.

Source: Declaring global variables in different tab