While I believe a formula has some merit, often it bogs down a program or a candidates ability to create a job effectively. While there need to be some guidelines, one must remember each position is an individual thing with different needs and expectations. You need to be keenly aware of the size of your parish, what the council and pastor and families expect and so many other factors that often a written guideline and formula hinder the process.
Research is the absolute key.
Check other parishes, check other denominations, check facilities, negotiate office hour requirements and program offshoots you WILL be given etc. These are things we did here and it frankly allowed us to become very happy campers since we were well informed before we even applied or brought it to a committee. Also, one final note. It is best to negotiate to be responsible to ONE person, your pastor. If you are responsible to a committee or many committee members, then you are responsible to several personalities with so many different expectations that its difficult to please anyone.