Should I set up an LLC and get a business license?

[Derek Hagglof]

Hi, I'm have a few rental properties and I have built a couple specs and sold them. I am trying to get a little more serious about real estate now and I want to buy, fix, build specs, etc and I'm curious as to what some of the pros out there are doing for business entities. I currently hold my properties in a trust. Should I form a new business and an LLC to hold my properties? At what point can I become a real estate professional? Is it a matter of getting a business license so I can write things off?

Thanks for any help-

Derek