These are some great questions and some of them so complex, it would take way too much time and space to go into them deeply here. So, I'll provide a few pieces of info and let others chime in as they see fit.
First, chewing helps prep the body for digestion and so you want to be sure you are chewing something more often than not - whether that be meat or veggies, etc. is up to you.
So, in general I haven't bought into the Paleo diet nor any other fad diet for that matter, but I won't get on my soap box. Grains are not all bad. There is a lot of research showing health benefits of grains. it is important to chose the less processed, more complex-carb, ancient grains (gluten-free if intolerant) as these provide fiber and beneficial vitamins and minerals. You are correct, some grains have phytates that can reduce absorption of certain minerals, however this usually is only an issue for people who are deficient in the first place. If this is something that you are concerned with, then you may sprout or soak the grains.
There are some foods that enhance nutrient absorption and other foods that inhibit it...for some examples see this post here: http://www.nutriliving.com/blog/5-facets-digestion