Wheel weights vary in hardness, but in general:
1) 12 BHN
2) 18 to 21 BHN after about 3 weeks of aging. The temperature of the boolit when it hits the water and the temperature of the water affects final hardness.
3) All the stick-on WW's I've owned were dead soft....basically pure lead. Pure lead (no antimony) will not heat treat.
4) See answer #3
5) Properly sized and lubed, air cooled clip on WW's will work fine.