Could I substitute Israeli couscous for the rice? If so, how much liquid would I need and for how long woul should I cook it at 400?

I don't think the problem lies with the liquid needing to be adapted. The chicken will need a longer cooking time than the couscous, and the couscous really should be baked under a cover. You might be able to adapt it if you cook the chicken for about half an hour in the spices and liquid, and then add the couscous for the last 10-15 minutes of baking time. However, you would still need to cover the dish- so it sort of defeats the intent to get nice brown crispy skin on the chicken. If you are determined to use Israeli couscous, it might be better to cook that separately, and then serve the chicken on top of it. Keep in mind that the Israeli couscous is really a pasta, not a grain, and that means you have to cook it slightly differently.