After going through my stats with a friend of mine who is winning at 400nl, he commented on my low 3bet percentage (<2%) which he says allows my opponents to play perfectly since my range is so polarized to KK/AA. Although this has still been working fine for me, he suggested slowly widening up my 3bet range in position so i can become more accustomed to playing in 3bet pots which occur much more often as you move up

1) Which sort of hands should I add to my 3betting range if i'm "3betting light"?
2) Which players would this be most optimal against?
3) How should i size my 3bet cbet?