Just a 4 x 4 I was thinking more of a 10 x 4 bed for three large cherry tomato plants one or two zucchini and pepper plants. Would 4 x 4 be big enough??

One of the nice things about square foot gardening is that you can get much more out of a 4x4 plot then you'd expect. :) With the quality of soil/compost, and the lack of weeds, and a soaker hose on a timer, I've fit even more then what you are describing in a 4x4 with great results. I do however, keep tomatoes trained to a central leader. If you are picturing much more sprawling plants then I could see the space concern.

4x4 is not big enough. I had 2 healthy zucchini's take over a 4x6 bed on me years ago, I do not stake my zukes though. If you have the room and $ for filling it, go with the 4x10 bed. A 4x8 would be fine too. Just as suggested prior, trellis the north side of the bed, length wise 8/10 ft. Since it's cherries, I would assume your not pruning? If not pruning you do need more room than the recommended 1 plant per SQF. Second thought, the 8ft is fine, if you go longer at 10ft, your could fit more tomato plants.

In front of your tomato plants torward's the middle of your bed and front edge, I would place the pepper plants. I personally space mine at 1.5ft apart, not the 1ft. For me, the plants crowd too much for my liking at 1 per SQF, but that's just my opinion.

At each end of the bed/front corner I would do 1 Zucchini plant and torwards the middle/end of the season just train it to grow away from the bed, so it doesn't shade the peppers too much. This is as long as you have the room for it to grow outside of the bed.

Always a good idea to plant some pollinator plants if you don't have any nearby too.

I agree with some others here 4x4 is not big enough.

Tomatoes do not do well touching one another. They need room especially in a raised bed with nutritious compost they will spread out.

. A 4x10 bed would suffice,plus you could mix in some companion plants in with them all for natural pesticide.

I've been square foot gardening to some degree for about 5 yrs as well. I would say you can do it in a 4X4 space, but it may not be the best idea. I know it can be done, but it will set you up for a whole bunch of problems. I like to space my tomatoes to 1 every other square foot along the northern side with something small and leafy in squares between. I have found that there is a high chance of blight/other diseases if they are closer. Also, it is tough keeping a healthy zucchini to just one square foot. I have done 2x2 up a stake but 1x1 would be tough!!! peppers at one per square foot is a non issue though.

When my summer squash plants are happy they will take up 1 - 4x4 easily - tho I can put 2 plants 6in apart in the center. They are not vines and very bushy.