What XAML would produce this?

I created a sample layout of my project, and I'm trying to use XAML (with C# in Visual Studio 2013) to implement it.  My layout is somewhat wonkers (technical term).  This is my desired layout:
And this is my xaml code:

<Window x:Class="SODA.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="420" Width="680">
        <StackPanel Grid.RowSpan="7">
            <DockPanel>
                <Border BorderBrush="Blue" BorderThickness="0,10">
                </Border>
                <Menu DockPanel.Dock="Top" Height="30">
                    <MenuItem Header="_File">
                    </MenuItem>
                    <MenuItem Header="_Edit">
                    </MenuItem>
                    <MenuItem Header="Help">
                    </MenuItem>
                </Menu>
            </DockPanel>
            <StackPanel Orientation="Horizontal">
                <Label Content="Input File" FontWeight="Bold" FontSize="14"/>
                <Button x:Name="cbInput" Content="cbInput" MinWidth="93" Margin="10,0,0,0"/>
                <Button x:Name="cbEditInput" Click="btnBrowseWord_Click" MinWidth="93" Margin="10,0,0,0"
                        Content="Edit" ToolTip="Click to browse for Word Document Template" 
                        Width="100" />
            </StackPanel>
            <ComboBox x:Name="cbxInput" Height="30" IsEditable="True"></ComboBox>
            <StackPanel Orientation="Horizontal">
                <Label Content="Reference File" FontWeight="Bold" FontSize="14"/>
                <Button x:Name="cbReference" Content="cbInput" MinWidth="93" Margin="10,0,0,0"/>
                <Button x:Name="cbEditRef" Click="btnBrowseWord_Click" MinWidth="93" Margin="10,0,0,0"
                        Content="Edit" ToolTip="Click to browse for Word Document Template" 
                        Width="100" />
            </StackPanel>
            <ComboBox x:Name="cbxReference" Height="30" IsEditable="True"></ComboBox>
            <StackPanel Orientation="Horizontal">
                <Label Content="Output File" FontWeight="Bold" FontSize="14"/>
                <Button x:Name="cbOutput" Content="cbOutput" MinWidth="93" Margin="10,0,0,0"/>
                <Button x:Name="cbEditOut" Click="btnBrowseWord_Click" MinWidth="93" Margin="10,0,0,0"
                        Content="Edit" ToolTip="Click to browse for Word Document Template" 
                        Width="100" />
            </StackPanel>
            <ComboBox x:Name="cbxOutput" Height="30" IsEditable="True"></ComboBox>
            <Label Content="Messages" FontWeight="Bold" FontSize="14"/>
            <TextBlock x:Name="txtBlkMessages" Height="Auto" Text="This section for messages." HorizontalAlignment="Left"/>
        </StackPanel>
</Window>

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What do I need to change to have buttons align and the text block stretch to the bottom of the window with a scroll bar?
Thanks!