If you really want to use fresh basil, cut using the chiffonade method - but VERY thin. The only thing you have to be concerned about in adding flavor to this dish is enough salt. You will use more than you think - but of course, taste first. This is just one of those dishes that I wouldn't use fresh basil. I'd be more prone to use fresh flat-leaf parsley and a squeeze of lemon for brightness that usually comes from the basil. Again, thinking just leads to more ingredients that aren't truly necessary
You could use a few strands of chiffonade basil as a topping. If you have gray salt it would make a nice finishing salt. I still feel strongly that the dish is about the sweetness of the roasted tomatoes - bringing out the flavor with the salt.
Your appy sounds great! One of my favorite ways to utilize some of these ingredients is to slather the toasted bread/grilled bread with goat cheese, a little slather of homemade pesto, topped with slivers of roasted red pepper. I will definitely have to try your version. The red pepper flakes are right up my alley!!!!!!!!!!!!
And yes, cut the tomatoes before cooking. This way they have a chance to roast on all cut sides.