rc1 is release candidate 1
esp8266 package: Arduino Primo is supported from version 2.4.0 rc1 of the esp8266 core for Arduino IDE. To install it using boards manager, follow the instructions.
Buy a Wemos or NodeMcu and learn esp8266 Test what you need to OTA upload to Primo. Because with Primo you do not have the trial and error option.
And do not forget, use only the 2.4.0 rc1 version of the sep8266 Arduino core.