Sand sounds like a good idea for slugs. Would probably work around hostas, too. I used crushed egg shells around my hostas last year, but the light colored egg shells was sort of a visual detractor from the scene.
I absolutely LOVE the carrots/tomatoes book. I have a copy but couldn't find it this year (my home is in major upheaval) so I borrowed a copy from the library. Using it to plan my new veggie garden, but soooo disappointed that it doesn't really go into herbs, like soapwort and other unusual herbs.
Marigolds and basil definitely have kept critters and insects out of my tomatoes. And along the thinking behind the three sisters (corn, pole beans, winter squash), I used the carrots/tomatoes book to come up with the Three Cousins (sunflowers, vining cucumbers, watermelons). It's always done great for me.
I also did my garden plan on the Mother Earth News planner. It was free for a month so I played around a bit then I put it down on paper when I was more sure of myself.
And now that my month is expired I have loads of ideas and I want to move things around. I would definitely save some space if I planted the beans with the corn. And I planned to plant the squash and pumpkins right next to the corn as well. I'm convinced to give a try to the three sisters this year.