To assign 'ctrl-N' to create a new layer (instead of a new window), do the following:

Edit/Preferences/Configs/Accelerators

Comment out this:
CTRL N = ID_NEW_BROWSER
like this:
# CTRL N = ID_NEW_BROWSER

Then scroll down to where it says "%ifplugin layers" and add this before the 'else' statement:

CTRL N = layers(New)

Also, remember to close the active layer, it's CTRL-W.

Also can you please tell me how to make it so when I ctrl-click it opens in a new layer in background or shift-click it opens in new layer in foreground? This would be very helpful.