I don't know that much about Star Trek, but the way you describe the Federation it certainly sounds like an anarcho-communist utopia. I suppose it would depend on the state of private property. You can still have personal property - you know, stuff - under communism.
Mostly Federation Government is a mediator from what I've seen, and there is still private properity, the main driving force of the New World Economy is striving for self improvement and betterment of everyone in federation space.
On a planetary level the planets keep their own governments, cultures, ect, so long as they ascribe to federation ideals which are along the line of a more advanced version of human rights accords.
At the intersteller level the federation is pretty much in charge and deals with military, exploration, and research.
They have a Exec branch with a President who is elected (details aren't given in the shows) he controls forgien relations, and is the military leader, though indrectly. A Legislative branch with two representeves from each member species. They control the federal buracracy which is streamlined via technology (no filling out forms in triplicate ect)
and the Judical branch which settles interplanetary disputes and other such things (these were the guys who were sitting in chairs dedicing if the android Data from Next-gen would be concidered a living being, and federation citizan, or not. They eventually said he had rights.)