What sort of stilts are you using? How experienced are you with walking on them? For convenience and safety, I would probably make the scythe handle much longer so that you can use it as a walking cane while on the stilts.
For the scythe handle, you could use a curtain rod or a yard tool handle from the hardware store, Build up the knots with expanding insulation foam, carve them down to shape with a razor knife, cover with paper mache and paint.
For the scythe head, there are a dozen different ways to do it. I personally would do a core of Sintra or MDF, and blue insulation foam to build up the thickness. Cover with paper mache or seal with something like mod podge, the paint. If you're moderately skilled, come up with a way to make the scythe blade detachable from the handle, for ease of storage and transport.
For the gloves, I would probably start with big inexpensive welder's gloves such as these:
Shred the cuff and wrap the wrist with some twine or something. You might be able to use some of the cut-off cuff pieces to extend the fingertips to make them pointy.
The knees, it really depends on what sort of stilts you're using.
For the arms, I would do a tight-fitting brown shirt that you wear underneath the tunic; use an airbrush to paint on a lighter color paint to mock up the wood grain. The spikes coming out of the elbows - personally I probably wouldn't worry about them until you're done with everything else; they're a minor part of the costume.