If you're just starting to get comfortable with your materials, you'll probably want to work on getting your construction techniques down before trying to make the claws move. Once you've honed your skills with basic construction, you can move on to more advanced tricks like articulating the claws.
If you're wanting to carry it around a con, you'll probably have to modify the scale just a little bit to make it practical to carry, and so you don't get worn out after half an hour of wearing it. You can still make the claw big and huge (if you use lightweight materials), but you'll probably want to scale down the first "shell" segment so it fits over the length of your forearm, with your hand inside the joint at the base of the claw. If you try to make that first forearm segment really long (as shown in the first reference picture), it's just going to make the weight of the claw that much more unbearable to carry around.
If I was approaching this, I would probably make it in individual pieces, maybe with a threaded rod in the base of each of the claw "fingers," and a reinforced cavity in the front underside of the claw "hand" where you could use a nut and washer to bolt the fingers to the hand. This would allow you to construct it in many pieces, instead of trying to do the whole giant thing in one go, and also allow you to disassemble it for transport and storage. The rear of the claw hand would be hollow, with an interior handle of some sort (maybe just a length of PVC pipe) to allow you to grip and maneuver the claw.
I'm no expert in pieces like this, I'd probably make each claw "finger" out of layered blue insulation foam, hollowing out each layer to reduce overall weight. Then cover with a thin later of paper mache, gesso and sand to finish the surface, use sculpey or Apoxie Sculpt to make the tiny details (the spines on the back of the claw). Then paint.
Fortunately, the wide surfaces of the claw shell are relatively large and smooth , so the "big" parts of the foam sculpt should be pretty straightforward.