There is so much misinformation about spark plugs out there, and while it's the unknowledgeable enthusiasts passing it around on the internet and amplifying it, the tuners are the ones feeding the cycle to start with. Spark plugs are really simple devices and easy to understand.
Gap is simple to deal with, and the only reason it would be included in Whoosh's stage 1 recommendations is that if somehow plugs got installed with the gap completely off, like someone dropped them and crushed the gap, or they somehow got bent to a really wide gap, then performance will suffer for that cylinder. It's just to make sure they are at the correct gap, and the stock gap is correct.
Heat range is primarily where tuners and internet enthusiasts get way wrapped up over nothing. The rush to put "1 step colder" plugs on all the time is useless and a waste of time and money. You choose heat range of plugs based on the temperatures being reached in the cylinder. The stock heat range has been carefully researched for best plug choice. Changing your air filter element or putting on an aftermarket exhaust isn't going to require a different heat range plug, and changing to a colder plug will net you nothing but wasted time and money, and make it more likely that you will have fouled plugs and have to replace them again. The whole tuning scene results in people thinking they are running too rich when they see the fouled plugs, and so they tune leaner, but that isn't the problem. It's the plugs are too cold, and what they need is stock heat range.
Too high heat range plugs will result in overheating, visible at first on plug inspection, and can ultimately result in the electrode melting. That's not good either, but it will not happen with the simple things most people are doing with their engines.
The web pages on plug manufacturer's websites showing how to determine heat range for plugs are easy to understand, and have been correct for a century. There's a lot of experience, and it's mature technology. It's really simple, and the internet and "tuning" have served to misinform a lot of people. I know I won't convince all those guys out there who swear they can feel the huge difference in performance they got from step colder plugs, but it's just not true. Plugs can't get you "better" performance. Only correct performance.