Short answers, pulled from the story.
The Marburg Colloquy failed in 1529. This event defined early Reformed theology by its opposition to Lutheran views on the Eucharist while maintaining a spiritual presence of Christ as propounded later by John Calvin and Heinrich Bullinger.
Federal theology orders God's life with people primarily in two covenants: the covenant of works and the covenant of grace. The covenant of works is made with Adam and Eve in the Garden of Eden where terms require perfect obedience for blessed life, while the covenant of grace was made immediately following their sin offering salvation from death on condition of faith in God.
The World Communion of Reformed Churches includes some United Churches and has 80 million believers in 211 member denominations around the world. A 2011 report estimates that members of Presbyterian or Reformed churches make up 7% of the estimated 801 million Protestants globally or approximately 56 million people.
John Calvin criticized arguments against charging interest for money suggesting that walls and roofs of houses are barren yet permissible to charge someone for allowing them use. He qualified his view by saying money should be lent to people in dire need without hope of interest while a modest interest rate of 5% should be permitted in relation to other borrowers.
John Knox brought Reformed theology and polity to the Church of Scotland after spending time on the continent in Calvin's Geneva. Presbyterian churches are named for their order of government by assemblies of elders or presbyters especially influenced by this figure.