In an ideal world (e.g., wire have no resistance, power supplies are infinitely fast, no noise ...), you would not need the buffer capacitor and filter resistors. The questions is how far from ideal is your system. Every system is different and what you read where general guidelines that worked in a lot of cases.
Setup your system in a way that it is close to your final system, but you can still do some modifications. Then try and see what happens.
Let’s look at the buffer capacitor. If your power supply is reacting slow to a sudden increase in current e.g., switching on LEDs, the buffer capacitor can help by providing the necessary current for a short amount of time while the power supply increases the current flow. The same is true for the wire. If the power wire is long or/and thin it will have a negative impact on the ability of your system to react to sudden current changes. Short and thick wires have less of an impact and will reduce the requirements for the capacitor.
If your system is stable for long enough you are done. If you later find the system is not stable under certain conditions (temperature ...) you can get back modify it.