I'm going to build 4 x 4 garden boxes. How many tomato plants will fit in each box?
Certified GKH Gardening Expert
As for spacing, I would do one tomato plant in each corner of the box, so four in each box.
As for supports, I would recommend that you look into making concrete mesh supports. They are about the sturdiest you can have and will be the easiest to stake down for the wind.