Preparing wall for painting

I have recently stripped wallpaper banner thst went round the middle all around the room. Now there is layers of old paint and to the plasterboard. So I have different layers where wallpaper have been stripped. I was wondering what is best to do? Do I get easi-fill and skim it and then primer it and paint. Or could I use things like poly filla. Only trouble is, it is a large area as it's goes all around the room.