In response to your question below:
The unit system is strictly for the balance of what you have to raise.
When you create your projected annual budget, you put in all projected expenses, (those expenses which may or may not be, you also put them in, taking worst case scenario) You then insert all projected Income, those you know you can rely upon, Membership, High Holidays, Tuition, Program participation etc. (those items of income which may or may not actually materialize you don't put in, again taking the worst case scenario) Once you know your total projected expense and your total projected income the balance or the "deficit" becomes your fundraising goal (you can add some more to that number and round it up to match the unit you would like to create)
The amount of the unit should be what you feel you can ask and get from most of your better donors, so a Shliach just starting out would set as a unit not more than $1,200. Being on Shlichus several years you can make that unit $1,500, more years on Shlichus you can bring it up to $1,800 and so on.
Your top 10 or so donors you will ask to give multiple units as many as 20, 15, 10 and slowly work your way down.