3) How hard has it been to implement the D20 modern rules into NWN?

Different parts of the D20 Modern rules are approached differently. Wizards of the Coast actually released a modern D20 rule set based on the same open source D20 system NWN currently uses, the specific dynamics of the game has needed very little customization. The hardest hurdles ahead are implementing skills and firearms, given the current limits in the engine for modification. Understandable since Bioware never intended for the community to do more than just create fantasy modules to play in.