work-groups and work-items execution

I have a couple of beginner questions, my laptop's GPU has:

• 2 compute units
• a local memory size of 48 KB
• Max Work-group Total Size of 1024
• max_work_item_sizes:( 1024 1024 64 )

My questions are quite simple:

1. Those 48 KB of local memory are per compute unit or for the whole GPU?
2. If I only create one work group, does that mean that openCL won't use half of my GPU's capcity?
3. is there a relation between max work-group total size and max_work_item_sizes?

Thanks a lot for your help