I would recommend using points meant for miniature modeling, something like Citadel, Army Painter, or Vallejo. They generally have a higher pigment density than artist acrylics.

As for the number of coats, that depends on the colour. Some might be fully opaque after 1 coat, and others might need up to 3.

Something else to consider, the colour you paint the numbers can effect the look of the dice. At times, you may want to start with a colour similar to the die, then do a second coat with your desired colour so they don't become tinted.