How radical, in economic and political terms, were the Radical Republicans?

I would say they were quite radical in both categories. 
The political changes that occurred right after the Civil War, including the abolition
of slavery, giving freed slaves citizenship and black males the right to vote were very
radical acts, undertaken by most Republicans, radical or not.  But Radical Republicans,
led by Senator Thaddeus Stevens, also wanted to punish the South with the Conquered
Province Theory, denying them citizenship and treated them like occupied military
districts.  While this did not get adopted, it was certainly
radical.

Economically, Stevens also championed the "40
Acres and a Mule" idea of distributing former plantations to former slaves, first
started as a convenience by General William T. Sherman, and giving each family a mule to
work the land.  This idea was also too radical for mainstream Republicans and the
President who refused to adopt it.  The Freedman's Bureau, also strongly supported by
the radicals, did manage to function for six years after the Civil War bringing
education to former slaves in Southern States where it had once been illegal to teach
them anything.  200,000 blacks achieved basic literacy in just six years, a radical
economic, but also social act.