Arms needed all done in blender
Do you have some concept or do you imagine things “on the fly” ?
ive looked at lots of concepts for inspiration but never went off of any
Something is telling me this is going to be a really good project. I didn’t see it mentioned, but are you considering rigging and animating this?
I dont know but im considering it
Are you going to make it an old, rusted and damaged Mech? I was kinda hoping for a neat, shiny and detailed mech maybe with a few “battle scars”…
Anyway, I’ll keep and eye on this thread and is looking forward to see whats going to happen next 
What is the purpose of this machine??? Will be easier to give suggestions if you know what its for?
Belt driven hands don’t look like a best way to go…all it can do with that design is wave at people at the entrance to the shopping mall. 
I did a mech a few years back…have a look, MAYBE you will find something interesting.
http://www.blenderartists.org/forum/showthread.php?150182-lt-lt-Raptor-gt-gt&highlight=
Keep it up.