Squashes need a lot of room to spread out. Lots of people around here grow them separately from the rest of the garden. They're pretty plants (I think), so people put them around their mailbox, around the house or walkways, or just in random places in the yard.

With tomatoes, it depends on how much canning/freezing you want to do, and also if you're not a super-diligent gardener, yields can vary a lot from year to year. A dozen to 18 plants are enough for DH and myself, but for instance, this year with 10 plants (plus one cherry and one tomatillo), less than ideal weather and a distracted gardener, we got a total of 4 pints of sauce and no other preserved tomato products.

When you build up your beds, don't use treated or creosoted lumber. I would guess that the recycled plastic timbers should be safe, but I really don't know, so I'd want to read some more about it. In my own garden, rather than built raised beds, I just mound up beds at the beginning of each season. That gives me drainage and soil depth, but I can still till and amend the garden all at once, and build up a deeper and deeper topsoil year after year. But my soil is over clay, so that's different from rock...