If you need a full head kit, 50 to 70 individual dreadlocks will look natural (if you like more lush dreadlocks, go for a larger quantity). In the case of mohawks, I usually advise 30 to 40 pieces, it all depends on how high the sides of your hairstyle are.
I noticed that my clients usually choose 60 pieces of dreadlocks, about 1,2 - 1,5 cm thick.