A flat tax system is a much more fair and reasonable way to tax people because a person who earns 3 to 5 times as much as another individual shouldn't pay 10 to 20 times as much tax. On top of this the more "progressive" the tax system is the more likely it is for the system to be built around the concept of "Robbing Peter to pay Paul"; and the more "progressive" the tax system becomes the more loopholes are introduced which allow people to avoid their taxes. With that said, every person should have portion of their income which are tax free that represent the basic cost of living; say $15,000 to $20,000 per year.
Now, as for services the government should provide ... The government should only provide services when they're necessary services and the government is the only entity that can (Foreign Affairs, Military, Police, etc) or when the service provided offers significant value and the government can deliver them at (or above) the quality level of a private institution at (or below) the cost of a private institution. Education is generally a service that the government can deliver in an effective way, but in the United States it is failing in a pretty remarkable way.
