#5 knots should bleach easily. There are plenty of threads on the forums discussing the process.

Yes, the systems will look thicker before cut in. It may also seem dense after you first get it cut in. But once you put some product in it, whether gel, brylcreem, etc... the hair will separate and show some scalp when you style it. If styled dry(without product) it will appear more dense. Debby can thin it out some if you both think it needs it. Let her take a look at it and then get her opinion.