Joe

 Tokyo is great and if you've never been before prepare to be amazed.

About getting there, firstly if you don't like oppressive heat then DON'T go in August at all other times the weather can be quite clement. The flight is very long and in flight entertainment will be needed depending on the airline (I once got stuck on a 12 hr flight to Tokyo with no real in flight entertainment and it was a nightmare) so if you can afford it, take as many gadgets as you can (DS Lite, Portable DVD Player+DVD's, Books and whatever else you might need).

It goes with out saying that if you don't enjoy flying premium economy is a good option for a little extra money. As for your choice of departure airport I always find it better to pay a little bit extra to fly from your nearest airport rather than your nearest major airport, it might be cheaper but you regret the extra time you have to spend in transit to the larger and cheaper option.

As for landing in Narita. Tokyo is about an hour to an hour and a half away from Narita depending on which train you get (express ect ect) but I have found that now I'll book a stay in a hostel or hotel in Narita and travel to Tokyo a couple of days later when refreshed; trust me, after a long and uncomfortable flight, getting on another train to Tokyo for an hour and a half and then having to navigate Tokyo for the first time to find a hotel can be a bit much for even the most sturdy of travellers.

Well I could go on but the trip belongs to you so, enjoy!