Originally Posted by
mschuler
Does this seem like a reasonable approach or am I missing something (e.g., lockers are never available, etc.)?
It's possible. However, I'd suggest heading straight to Tokyo - Put luggage in a locker at a station and pick up at the end of the day when you go to Haneda. You'll waste less time in transit and less money on fares.
What do you want to see / do during the day in Tokyo? That would determine where to leave your stuff.