I firmly believe in executing contracts for any working relationship, in or out of the church, whether volunteer or paid.
I always recommend client churches to put all their staff (paid or unpaid) on contracts. It clarifies and "sets in stone" the expectations of the employer and the employee, and can be modified as needs or expectations change.
Your agreement (contract) should include your role, responsibilities, expectations, and the employer's expectations of you. This, of course, includes your salary, any disciplinary procedures, benefits, etc.
It does not have to be a 13-page document, nor does it need to be full of a bunch of legalese (although it is helpful to have an attorney review it for legality).