[quotename BlueFalcon]The hardest AI is Expansion Insane Terran/Zerg/Toss.[/quote]
Do they require starting units and a special amount of resources? or do they play like melee?

The staredit help says that Insane AI will build all unit and technologies, so I presume you would only need a main tech tree building (ex. Command Center, Hatchery, Nexus) and a worker if not four.

The Custom AI (I.E. Expansion Terran Custom, Zerg Custom, etc.) plays like melee. The Easy, Medium, Difficult and Insane scripts, as well as the ones built-in for the campaign maps need more starting resources (usually 3000 of each is enough).