Great video Dina and fabulous samples!
Can I add just one thing to your commentary? You're right that you can use pretty much anything over anything else to add shading but the one thing you shouldn't do is use an alcohol marker (Copic' Spectrum Noir, ShinHan etc) over a waxy pencil (Prismacolor, Derwent Colorsoft etc). The solvent in the ink will "dissolve" the wax base of the pencil and you'll gum up your marker nib. Doing it the other way round is great though (pencil over the top of a marker base).