We know 2.5% is not in the Quran but I fix the zakat amount according to:
2:219 (Certain things that hinder humans from attaining the aforementioned Noble Objective are now mentioned.) They ask you (O Messenger) concerning alcohol, intoxicants, games of chance, and gambling and money earned without labour. Say, “There is great detriment in these things as well as some benefits for mankind. But the detriment of them is much greater than the benefit of them. They drag down the individual and collective social potential.” And they ask you what they should give. Say, "All that is surplus." Thus God makes His messages plain for you, that you may reflect.
Whatever is excess to the needs of individuals are invested into society so that everyone benefits.
Soum has verses that say eat and drink until 'dawn' so we may stop 'abstinance', if we want to do, undertake a training period.
Hajj has few requirements according to the Quran so all the rituals have been added by our ancestors ans we know what the Quran says about following them!
The biggest requirement of the Quran is to gather MANKIND to show them the 'signs' of Allah which is the practical implementation of the Quran, totally devoid from the modern hajj and instead they want to stone idols to satan.