\def \username {Sage Vaillancourt}
\def \thecompany {BananCorp}
\def \jobandpronoun {PusherBoy }
\def \skilltypes {broad, practical }
\def \myskills {software design principles }
\def \closingtext {I am looking forward to hearing from you}

\def \body {
    My name is \username.  I would like to work as \jobandpronoun with your
    company.  I think my knowledge of \myskills will contribute well to your
    team.

    I am passionate about my work, and think we would work well together.

    Thank you for your consideration.

}

\documentclass[12pt]{letter}
\signature{\username}

\longindentation=0pt
\begin{document}
\begin{letter}{}

\opening{Dear \thecompany,}

\body

\closing{\closingtext,}

\end{letter}
\end{document}