Depends what you mean by portrait...
Welcome, wouter... :cool:
As I've often said, portraits can be anything from a headshot (or even tighter) to having the person small in the shot as part of a much larger environment.
The size space you describe is large enough to do a lot of different kinds of shooting. And if by portraits you mean headshots, that yes, it should big enough...
As for lighting, there should be quite a few threads in this forum dealing with basic setups. To start, a couple of halogen hot lights and maybe a compact off-camera flash unit would be enough to get you going...