Starting with AK is a good idea, one of the most common gun types, and parts or upgrade will be easy to find.
You can take a look at the CYMA AKs and Cybergun AKs (Basically, still CYMA AKs). CYMA makes the best low end AKs.
I am not going to repeat about the metal bodies... I would get a metal body one consider the price difference is not that big.