Yeah those are the right kinds of things to randomize. Changing the note’s start will be more effective than length.
Velocity is great, unless the instrument doesn’t respond to velocity or only has a few layers so the sound never varies. So check first that it will do anything noticeable. Same with cc’s - make sure varying them does something useful. Also with velocity make sure to do accents (i.e. increased velocity on accented beats) first which makes it sound more musical than randomizing will.
Also it is better to randomize by a small amount several times than by a larger amount only once. For example randomizing starts & doing it multiple times will cause the randomization to cluster around the quantize beat in a normal distribution. This mimics how people actually play - we’re always aiming for a specific moment and miss by a bit & occasionally more than a bit. Most of my LE Presets that do randomization tend to go -3 to +3 from the current setting, assign it to a key and repeat to increase variation.
My drum programming took a huge leap forward when I stopped quantizing when entering hits/notes. I zoom in to one measure and eyeball where to put the hit, listen and move if needed (but typically don’t need to). This also lets you do stuff like put the 2’s and 4’s just a bit behind the beat. So I’d encourage you to play around with not quantizing in the first place.