Once a week or so should be good. Don't do it too frequently. Oily skin can be treated with masks more frequently, about two to three times a week. Yogurt can be good for oily skin due to its tightening properties.
You should do both. Washing your face first gets rid of the excess dirt and oil, making the mask more effective. Washing your face afterwards gets rid of any residue...
Try writing down what you learn in a notebook! Some people find that they learn faster when they write everything down. Practice writing down your English-Spanish vocab, as well as...
Either! Both are totally acceptable. If you want to look more realistic, then paint your face. For a scary clown like Pennywise, a mask could be better, depending on the...