You'll get differing opinions on this, and the soil depth will be the deciding factor - in my opinion. At a soil depth of 6", I'd put no more than 4 plants in that 4x4 box. If 12", I'd plant 8. Trellises (2) located a foot in from the north - and south sides is the way i'd do it.

EG

Because I am lazy and have the room, I grew my indeterminate tomatoes in 18" diameter cages made with concrete reinforcing wire. I put 5 plants in a 4X6 foot raised bed that's 12 inches deep. One plant roughly in each corner and one in the middle. Worked great. The only pruning I did was removing the bottom few branches and suckers. I grew determinate tomato plants in homemade self-watering containers.

You really should get and read a copy of the SFG book for reference. Basically, plant four indeterminate tomato plants in four square feet, trellised up the north side of your box. Then you still have twelve squares (in a 4' x 4' box) for planting other, shorter crops.

Do an internet search on how to prune tomatoes, or check the tomato forum. There are some really good web pages with detailed diagrams outlining the ways to prune.

I thought that my indeterminate vine tomatoes did pretty well last year using that 4/4 layout.

I also did a box of determinate bush tomatoes, where I planted five plants. It turned into a huge tangled mess of tomato plants where blight thrived and the tomatoes did not.