each coil is above each cylinder... the order doesn't really matter

if you're getting a po300, its random misfire, probably not any particular plug/wire/coil.

If its a Po30# that cylinder has mis. (be it plug/wire/coil). I'd do plugs/wires first. Especially with your mileage. If you still have a light, and it's a specific cylinder try the coil. Could also be an injector, thought kind of unlikely.

check your pcv, if that year still has one. I checked my moms other day, and it was missing the check valve...explains why her truck has been going thru oil between changes. That's only thing I can really think of that would cause "soot" unless you accidentally put diesel in it