1. I believe they are perfectly graded because each one of them suits the level perfectly.
1. Beginners : wall, picture, chair, room, hall
2. Intermediates : living room, upstairs, air condition, book case, blanket.
3. Advanced: neighborhood, apartment, dining room, elevator, landlord
3. I would choose: optimistic, intelligent, stubborn, easy-going, insecure, calm, hardworking ( I would choose these words to describe someone’s character and also for intermediate level. They are not that hard or easy, they just fit the level.
5. Choosing words depends on the levels of student. For beginners teacher should choose the words for them since the new language is knew to them. As for other levels they can choose the words by themselves and what do they desire to learn.