You don't need to feed the plant now, if your soil has plenty of organic matter in it. If your soil is poor, you can amend it at planting time.
And that's it. Stand back and watch your tomatoes take off. A word of caution, since this planting technique encourages your tomato plants to send out lots of roots, they will be difficult to pull out of the soil, at the end of the season. Still, it's a small price to pay for healthy, productive tomatoes, don't you think?