Well if it isn't too late.. if your clients hair will curl at all, I would put some kind of curl into it just so the little hairs that might poke out of the braid wont be super straight, use a light pomade that isn't too sticky so you can control the fly-aways and keep your sections clean. Id suggest to wash and dry your hands so they are free of product before you pull the braid out more to give it that fat look, without having hairs stick to the product that might be on your hands or accidentally pulling it out too much
And for the bump at the top of the braid, I would personally back comb that and pin that into place and then do the braid from there so you don't end up pulling it down flat and then having to try and get body out of it after .. hope that makes sense and helps!