Stick with stock plugs... these motors don’t like much else, same for coils... cleaning a MAF is always a hit and miss. I’ve had more die, than get better after cleaning. Might be worth just replacing. It would also be helpful to see if there are any associated codes stored. You can get codes without a CEL, though usually if there is a fueling issue it will throw a CEL. Any OBD2 reader can pull basic codes.

Also, rattling with a cold start for a second or two, can be normal, the chains make some pretty good racket when kicked in, but it could also be a sign of failing/weak chain tensioners. Hard to tell one from the other. If it doesn’t persist and the “rattle” is very brief, probably not a big deal. Mine does it, particularly after sitting for a few days. Otherwise my engine is very, very quiet.

“Proof” no... seeming general consensus? Yes. Either way, I too have been doing this car thing for the better part of 35yrs. In my experience, the plugs that are stock in most engines generally work best, (not always) Sure, NGK’s are great plugs... for some cars. My Jeep runs like **** on them. You will be fine most likely, but I look at it from the perspective, Beru’s work, they are a known quantity. Doing the plugs on these isn’t hard particularly, but if another plug doesn’t work well, that’s just double the hours, vs one and done. K.I.S.S. (Keep it stupid simple) always... if possible!