well low layer heights arn't necessarily a good thing. I pretty much only go down to 0.2 mm anyway.
Slower printing though is necessary for small parts as is active cooling. It also helps to print more than one piece at a time, to give more cooling time between parts.

Smallest things I've made to date are 5mm 8 toothed gears and 3mm rubber tires.
The gears were made from colorfabbs xt(petg) and the tires from flexismart flexible rubber.

I didn't need a brim for them - but it an be useful if there is on;y a small area in contace with the print bed.

I don't use abs :-)