First off, Vap's are awesome!!! So good choice there. That being said, a little medicine will go a long ways in a vap, depending on a few things. How high you set your temp and how dry your herb is. And yes you can use the left overs for cooking, or other extraction methods.

Also, smoking from a vap is very different from other methods. First of all draw slow, you may see a slight white smoke but it should be nearly clear. You will taste it when you exhale. I should be a sweet kind of herb smell.