Form an LLC?! How do I knows its a DEAL?!

All,

  My name is Joel and I am BRAND NEW to real estate. I'm looking to purchase my first property and need some serious help.

1. Should I form an LLC prior to purchasing a property?

-I've heard that the tax benefits make it worthwhile and that i can run a number of expenses related to my property through the LLC as tax deductions (phone bills, miles, etc).

2. How do I know its a DEAL?

-I'm interested in buying a multi-family home to use as a primary residence and rental. Should I buy a "condemned" property or are they too far gone?

How to I gauge the strength of a rental market? 

Thanks!