Fleet Parking: 
If you have a fleet you have to have a place to park it.  Depending on where your business is located this could be an expensive proposition.  Consider indoor versus outdoor parking.  Outdoor parking could expose your vehicles to inclimate weather that could cause damage.  However, outdoor parking could be cheaper.  If your fleet consists of heavy construction equipment outdoor parking is the best option.  If your fleet consists of sedans and SUV's then indoor parking is preferrable.

Daily Management:
Think about how you would manage your fleet on a day-to-day basis.  Do you need a fleet manager? Do you need fleet management software?  You have to manage your fleet to track how much miles each vehicle is accumulating, determine when vehicles are due for service, get vehicles into maintenance when damage occur, track fuel utilization, deal with accidents, etc.

Lifecycle Management:

You have to manage each vehicle in the fleet throughout their lifecycle.  That means that you have to manage the new vehicles that come into the fleet.  You have to set a replacement timeframe for each vehicle.  That means you have to set replacement timeframes at between 2-5 years.  You have to determine who will provide the maintenance service on your fleet.  Many dealerships provide this service as part of a lease contract. 

Unforseen cost: 

There are also unforseen costs such as traffic tickets, tolls, vehicle cleaning, parking at event sites when your employees travel to visit a client or conduct business, etc.  You have to address how you will deal with these costs.