At first, start from reading the XtraGrid documentation. Then use the DevExpress Support Center.
Anyway, here are some answers:
XtraGrid does not actually display data by itself. It uses Views to represent data. You can refer the View itself or refer to the GridControl's main View using the GridControl.MainView property.
DataGridView1.Columns(12).Visible
All columns are stored in the ColumnView.Columns collection. Use the GridColumn.Visible property to specify the column's visibility.
DataGridView1.RowTemplate.Height
You can set data row height manually using the View's GridView.RowHeight property
DataGridView1.Rows.Count
Use the GridView.RowCount property.