Madu,
I strongly recommend you re-think your management strategy. Owning rental properties in the Metroplex is a great idea. Managing them remotely, not so much.
Look for PMCs that have been in the PM business and have a large enough client-base that you feel comfortable using them, who can provide all the services you need, and who are paid based on performance.
As Kyle mentioned, you should expect to pay 7-10% of what they collect, as well as 50-100% of the first month's rent when placing new tennants.
I suggest you visit with Suzette Teague (817) 996-1772 (our club's Property Management sponsor). If she cannot meet your needs I would also recommend Kyle (previous poster). I have known both for several years and believe they can both handle your PM needs very well.
Let me know what else I can do to help you grow your business.
-Greg
Greg Wilson
The REI Mentor