6" is fine, but more doesn't hurt ;-) Plant roots will grow right through the newspaper without a problem. They will also grow into the soil below so depth of the raised bed isn't as critical.

You can grow all the plants you mentioned together, but peppers and tomatos share diseases and cukes/cataloupes share some of the same pests like cucumber beetles.

If it isn't much problem to build another bed and provide some separation then do so, but otherwise don't worry about it. It's not normally a big deal.

Thanks! I thought the roots would grow through the newspaper, but I wasn't sure since it's purpose is to keep grass and weeds out. Does it decompose by the time the roots get to it?

I will plan on doing 6 to 8 inches then. Cost is a factor right now, so the less soil and edging I have to buy, the better. And then maybe I can afford to do 2 boxes to separate them.

Thanks again!!!

The newspaper stops most vegetation growing up through it because most vegetation is flattened and smothered when the paper is initially laid down. As soon as the paper gets wet though roots have no trouble working through it. If you have ever picked up a wet newspaper you will understand just how easily it falls apart.

I really think that the depth is dependant on the vegetables that you are growing in a particular raised bed. Most all of my beds are 6" deep and so far I haven't had any trouble growing anything in them :-)

This year I will have one bed that I'm going to dedicate a spring planting of corn. The bed is going to be 3x14. I am going to double up on the depth (12") since I've read that corn needs more nutrients and deplete the soil pretty fast. So hopefully this will give the corn access to more of what it needs in the deeper soil mix. Also, from what I have seen in the past, my corn roots have grown quite deep.

Now, as far as cucumbers -- I've had no problem at all growing them in 6" deep beds. This was plenty for them.

Here is a link that might be useful: Judy's Square Foot Garden Blog