Regarding playing technique, I do two different types of tremolo (well many more than two). One version, I do an exact number of down-up strokes per note, so a short tremolo might just be down-up, or DUDU or DUDUDUDU and so on. The other version, there is no fixed number, the aim is to blend the strokes so smoothly that there is no associated counting, other than the musical tempo itself.
Another part of the technique, vary the angle of the plectrum as it hits the strings. If the pick is angled at say 45 degrees to the strings, it will glide more smoothly over the strings, and gives a soft, somewhat muffled tone. Altering the angle up to (or even beyond) hitting the strings with the pick flat on to the strings gives a louder, brighter more emphatic tone, but can be harder to play smoothly. Do both, do all of them, vary the angle. It's all about drawing out that wonderful expressive mandolin tone. No need to do things just a single way when there are lots of ways.