My goal is to make things "water tight", and as low poly as possible.

A well modeled object can always be increased in polygon size with a sub d modifier. Getting it lowered again is a nightmare.

mo·nop·o·ly  [muh-nop-uh-lee]
noun, plural mo·nop·o·lies.
1. exclusive control of a commodity or service in a particular market,
or a control that makes possible the manipulation of prices