A: Building a full, brand new rusEFI board from scratch is probably an exercise in insanity. We already have too many different hardware configurations, and are running a bit thin to support it all. Please consider basing your P&P design on Hellen, Proteus, or microRusEfi - either as an adapter board, or at least as a custom PCB with shared schematics.
Q: What EDA are you guys using for your open source hardware?
A: rusEFI preference at the moment is KiCad 5. A few legacy pieces are still using KiCad 4. While many EDAs have many cool features KiCad gives rusEFI uniformity and consistency.
A: There is no single right answer. It really depends on what kind of electrical signal is your tachometer expecting. Is it low-side driven? +5v logic signal driven? +12v logic signal driven?
Q: What are these four LEDs?
A: Many rusEFI boards have four status LEDs. All four LEDs blink on start-up just to confirm life.
Blue Communication LED which is expected to blink at 50% duty cycle during normal board operation.
If USB communication cable is connected Blue LED starts to blink faster.
Red CRITICAL (previously known as FATAL) error means you have a CRITICAL error, engine operation is not possible with CRITICAL error.
Green LED on many rusEFI boards is RUNNING. Off if engine is stopped, blinks if engine is cranking, solid if engine is running.