dentedcapacitor

1) yes it will work
 
2) lanes is just a name for bandwidth
a GPU will use as much bandwidth as it needs
usually it uses about 8 PCIe2.0 lanes (same as 4 PCIe 3.0 lanes) but nvidia gpus need at least 8x to work
when you go down to 4x 2.0 lanes you can start to get a performance bottleneck
 
this is why you can have multiple GPUs running at 8x and there will be no performance decrease

1.) Yes, it'll work just fine. PCIe is backwards and forward compatible with all generations.
 
2.) All 16 lanes are still used.