Infinite

I don't think there's a right answer for this. I can have anything from 1 layer up to 4 or 5 over different octaves. Depends on the style you're going for. If it was Hardcore or Hardstyle etc they tend to use a lot of layers to make a huge sound. Some Makina tracks have very basic leads especially in the old Spanish, like this one For Spanishy stuff I usually have a Supersaw layer for the power and then another lead or two to give it character, like a voice stab (like in the video above) or a flute, guitar etc something interesting. I might have the bass notes in the melody or I might run them through another sound so I have more control over them, or I might not have the bass notes in the melody at all. For North East I might just have a big digital sounding lead without the supersaws. It's really up to you and what sounds good.