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.
See also https://github.com/rusefi/rusefi/tree/master/hardware
Q: What pin do I use for tachometer output?
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?