It's super-deformed so sorta open to interpretation, but the belt looks to me almost like a simple rope-belt. Something like simple 1/2'' cotton rope, the ends whipped with string (look it up). If you want to make it more brown, just boil it in a pot of tea. Make those loops from muslin with the edges folded inward, or use smaller bits of rope. Wrap the rope around you 1.5 times, and you can probably get away with just fastening it with safety pins at your sides.
The "strange gray cuffs" would probably be considered bracers. I'd do them so that both the metal part and the brown part with the circles is a single piece, but separate from the gloves. I'd do it as a sheet of craft foam, with more craft foam glued on top for the metal parts. I like spray-glue or contact cement best, since it's nice and flexible. Glue it up while the sheet is bent around in a cylinder, or it won't want to hold it's shape. Coat the entire surface with a couple coats of white glue, then paint it. Fasten it around your arm with a strip of Velcro. Yeah, a seam-line will show, but it's not a big deal.
I'd use the same technique for boots. I'd probably sew up a simple brown fabric boot-cover, and glue the yellow metal pieces and the leg bracers to that. The yellow piece on the toe might need to be heat-formed a bit. heat up an oversized rectangle of craft foam using a hair-dryer on high (or heatgun, or toaster oven if careful) and once it's all floppy, stretch it over a boot so it matches the toe shape. Then cut out the actual shape.
It could be interpreted that the yellow diamond thing is supposed to be attached to a necklace. Possibly the bars on either side as well. If you go that route, sculpey would work just great for that.
For the star-shaped bits of the staff, you can cut out the shape from a sheet of craft foam and glue that to the styrofoam, or to save money, you could use card-stock (I use cereal boxes). To make it symetrical, you'll probably want to apply it to both sides of the ring, in such a way that they meet together at the points.
For the styrofoam, go with the smooth expanded foam that's used to make ice coolers, not the rough open-celled foam. If you're stuck using the open celled foam, you gotta do extra steps to get a smooth surface.
For the sake of durability, you really should apply paper mache to the surface of the styrofoam. This will also help to secure it to your broomstick. About 3 layers of newspaper, squeegie out all the excess paste, and avoid air-pockets at all costs. Once dry, sand the surface with 220 grit sandpaper, optionally brush it with a last coat of white glue, apply primer, and then paint.