1. How can I display the ErrorProvider icon and tooltip in a row or column header (Microsoft's DataGridView can achieve this and more with its 'ErrorText' properties) ?
Currently you can use ErrorProvider with FlyGrid.NodeCellChanging or another cell validation notifications. We'll improve error diagnostics to the nearest FlyGrid.Net update.
2. How can I embed a control (a button for example) in a row or column header?
Currently FlyGrid doesn't provide winforms controls embedding, if you want to use buttons in FlyGrid, you can use ButtonColumn, see the Xtras\\TaskManager sample, that shows usage buttons in the nodes/rows.