The mk 1 bolters are made of finegrained plaster so they are impossible to drill out. Blonde haircolor was painted as its easier to paint it in one go, second squad gonna be red and brown colored heads in.
The squad really looks good, but I think for the 13th company, their armour looks too clean and new. Some parts from salvaged chaos armour (or just their paint) would surely give them a more distinct look. Otherwise, nice conversions and a good paintjob, your army surely looks nice on the battlefield.