I have a couple 2x6 and 4x6 beds that can hold a decent amount of plants, but it will depend on how you plan to prune them and cage/stake them.

Here's some of my beds

I had 3 tomato 3 zucchini and a couple of basil plants that in a 6x8 raised bed last year and people told me it was overcrowded

It depends on the variety/type of tomato plant. The general recommended spacing for tomato plants is 3 feet but there are many different size tomato plants. Some are quite small, some medium sized at approx. 4' tall and 3' wide, and many are huge easily 4' wide or more and 8-10' tall. So what variety are we talking about and how do you plan to support/cage them and will you be pruning them to a single stem or not? The type of support used and the amount of pruning done determines how close you can space them.

Zucchini plants normally require approx. 3 sq feet each.

If I was going to build a new bed for those plants and didn't want any overcrowding limitations on their growth then I would build it 4' wide so I could reach the center from both sides and at least 16' long because I use tall cages for my plants and do not prune them. However I would never plant 3 zucchini plants either unless I wanted to give lots away. ;-) 2 plants is more than enough for a family of 5 so I'd rather use the space for another tomato plant or some other crop.

Dave

For tomato plants we like the large cherry type. And I do use tomato cages last year plants got to be about 4' high and do not prune much

Just go 4x12' , that's enough for 3 tomatoes 3 pepper and 2 zucchini. Probably be able to squeeze some bazil

Problem is Frank "large cherry type" can mean many things. Most cherry tomato plants are huge easily topping 4 feet wide and 8 feet tall. But they produce hundreds of smallish cherry sized tomatoes.

But there are also some so-called "large cherry" varieties that are relatively small plants but produce fruit that are 2x the size of normal cherry tomatoes (aka salad tomatoes). Variety name tells us exactly what to expect from the plant. Can you be more specific? Know the name? You have grown these before? How big/tall did the plants get?

Dave

First time growing large cherry I would say maybe 41/2 feet tall forgotten the name though,

Gee, do you suppose on August 8th I could sneak some SVBs onto my neighbors porch? They can explain why I don't have any zucchini to leave! I can see it now. A little cage with cute little moths. Maybe with a butternut squash next to them.

HA! I'm sure with SVB you're done with your squash by then! We don't get them as far as I know! MANY squash in August! Nancy

My bed is 2.5 x 6 feet and I usually do 3 tomato plants. 2 will be ideal but that is the space that I have and it has worked fine. Nothing beats than trying it yourself. Zucchini I did 3 plants in same size and we had lot of zucchini to eat all summer long. Peppers I usually do 6 plants if not more in that much space.

I had 3 tomatoes and a zucchini in my 4 x 8 raised bed last year. Too squashy. 3 tomatoes and a row of lettuce across one end is better.