Carapils will help with head retention. Not going to do too much for body, you would be better with some Aromatic or melanoiden malt, or some Munich. Wheat can be good, and helps with head retention, and a little body, but it does not add any malt flavor, so using a lot of wheat in place of malt grains, will give you less flavor.
When I started, I found a lot of my beers were 'thin' or lacking something. I don't know what it was, but I kept going and pretty soon my beers became 'fuller' and more satisfying. 25 years on. and I still have no idea what changed to go from making 'thin' beers to balanced beers. I guess I just became a better brewer.
Unless you are using Carapils to get a certain characteristic in your recipe, don't go over 0.5 lbs in 5 gallons (~5%)