12V to 5V 3A DC-DC converter recommendations. WS2811 LEDS
The most likely reason for the 1000µF recommendation is to get the buyer (who has never heard about &quot;regulator transient response&quot; or &quot;capacitor ESR&quot;) to put a big enough cap, with low enough ESR, to ensure the voltage remains within the correct range no matter what power supply, regulator, or wiring they use. Because customer support costs money, and money is expensive, it's understandable the seller advises a foolproof solution.
Murata datasheet for your converter says &quot;Maximum Capacitive Loading 3000 μF&quot;, so it'll be fine with a 1000µF cap. If the 1000µF cap is too big to fit inside your LED strip aluminium profile, you can use a lower value cap... but then it will have to be a low-ESR cap, which may be more expensive than a 1000µF &quot;general purpose&quot; cap which has the desired low ESR and ripple current capability simply due to having high capacitance.
Looking at the figures at the bottom of page 6, transient response looks to be pretty good and fast, only deviating 0.25V for a 2.5A load step with a 10µF ceramic output cap. So it will also probably work fine with a 10µF ceramic cap.

What is the prefered type of DC-DC convertor for this type of project?

It should have quick transient response to keep the output voltage stable as LED current varies due to PWM dimming. Your Murata part is a good choice.