Unless yours is one of the troublesome hybrid chip failure ECU's (most are long gone as the failed many years ago...except in Art's fleet), I think the spare ECU is overkill. Even then, the simple jumper wire test can get you back on the road and confirm the ECU failure.

That said, LH 2.4 ECU's are plentiful at the PnP's unless you have a weird combination like EGR and pulsair (even then, I found TWO recently). I would consider a crank position sensor more crucial.

AMM is a must and it needs to be run in your car for a couple weeks, preferably in the hottest point of summer, to be considered "known good".

Power stage rarely fails as well if the thermal paste is renewed ever 50K miles or 10 years...whichever comes first.