Controls on other ascx

Well, in answer to the first part, here's an example(and keep in mind there are a few ways of doin this, this is just one way).
MyUserControl.ascx

VB Code:

<script language="vb" runat="server">
Public Property TurkeyName() As String
    Get
        Return  _TurkeyName.Text
    End Get
    Set(ByVal Value As String)
        _TurkeyName.Text = Value
    End Set
End Property
Public Property EatStuffing() As Boolean
    Get
        Return _EatStuffing.Checked
    End Get
    Set(ByVal Value As Boolean)
        _EatStuffing.Checked = Value
    End Set
End Property
</script>
<asp:TextBox 
    ID="_TurkeyName" 
    Runat="server"/><br />
<asp:CheckBox 
    ID="_EatStuffing" 
    Text="Do you eat stuffing?" 
    Runat="server"/>

MyTestPage.aspx

VB Code:

<%@ Register Tagprefix="Thanksgiving" Tagname="Turkey" Src="MyUserControl.ascx" %>
<script language="vb" runat="server">
Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
    MyTurkeyDayControl.TurkeyName = "Chris"
    MyTurkeyDayControl.EatStuffing = True
End Sub
</script>
<html>
  <head>
    <title>MyTestPage</title>
  </head>
  <body>
 
    <form id="Form1" method="post" runat="server">
        <Thanksgiving:Turkey 
            Runat="server" 
            ID="MyTurkeyDayControl"/>
    </form>
 
  </body>
</html>

As far as a global variable, the the Application object still exists, so maybe try that. Where appropriate I also use the appSettings section of the web.config file.