I have used the Earthbox, which I can plant two tomatoes per box, as well as, 2 peppers in the another box. However, I had to rig a support depending on the type of tomatoes, a determinant variety that has a limited growth requires a smaller on, whereas, the in-determinant will continue to grow and requires additional vertical support.
Prior to planting the vegetable incorporate 1 pound of lime throughout the soil mix
To plant the tomatoes, you dig a whole that is lowest where the root ball of the plant is, gradually increasing the height to the surface removing all the leaves that would be covered when you fill the soil level to the top. The stem that is buried will produce new roots along the stem.
As far as fertilization, I use an organic tomato/pepper blend that is 6-2-3, and apply a band across the container equal to 1 pound for the whole season.
Your source for Earthbox is Earthbox.com, and you can buy a package that includes fertilizer, Lime, and a flexible plastic cover.
I have started to build my own container with 18 gallon totes, but found it necessary to purchase a plastic underwater basket at Lowes and cut out the cover to fit above the basked & drill holes to permit the soil to soak up the water that is stored in the bottom. Must drill a whole just under the lid in the sides of the container to permit excessive water to drip out & signal when you have adequate water for the plants.
Icidently, GardensAlive is a source for organic fertilizer & insect & biofungicides.