People grow produce around Haneda airport so your imagination may be flawed, but either way, an agricultural economy, while important in its own way, is not going to slow population loss to the cities.
No they don't. The part that's not ocean is an industrial wasteland; if you did manage to grow anything it would likely be too full of heavy metals to safely eat. You're probably thinking of Narita, which despite billing itself as "Tokyo" is 50km the other side of the prefectural border.
Not disagreeing (I'm sure you're right that he's thinking of NRT), but theoretically, you could grow stuff in an industrial wasteland without it being contaminated: you could build hydroponic facilities or some other buildings, ship clean soil in (for raised planting beds for instance), and grow things there. Just don't use the soil in the ground.
I imagine it's just not worth it to go to this trouble to grow things on contaminated former-industrial land.
