A recurring entry from a former novice fishkeeper.
The nitrogeon cycle is not something to joke about. Could you imagine if, in the formation of the world, we had accidently added just one OCCEON of fish too many? Well that is effectifly what we are doing when we do not properly wait for the nitrogen cycle to take place. This cycle is the backbone of the entire livelehood of everything else that will come into your tank, and should be researched. YouTube has some great videos on this topic. Let me put it this way: like all sciences, fish keeping is not perfect; but it is being perfected. That means that when a Local Fish Store (LFS) recommends you wait before adding fish to a brand new tank, it is because they themselves have probably added too many fish at a single given time. As aforementioned, if an entire ocean of fish were added before the plants, we would not even have plants as they are on this earth. This is what you are promising a new tank to have: different type of life. Not just the one you wanted, but something different. Now that may be good, may be bad, but either way, please remember that when you start something new, planning is always better. Like my Grandpa always told me: measure twice and cut once. Well. Check that Ph 67 times and add in your favorite fish at the end. I was too once like you, more excited by the hope of what my fishtank(s) might become, instead of waiting for what I could make of them. This hobby of keeping fish, in an aquarium, under exact conditions, could be taken as a daunting task for even the most novice of world creators: so don't be afraid to make mistakes. Most importantly, however: don't be afraid to WAIT to make mistakes.