Import data from source to target

Well, I think I solved my own riddle and really not surprised I did not get any responses here as I'm sure I was too wordy above and not clear what I wanted to really accomplish however, thus far, the below code does what I want it too and still testing a few mock scenario's. I tried to use a varied range for the Source Workbook by row counting the source but, kept getting the error noted and left in the code along with the code lines I left as comments where the error was occurring. If anyone can help solve the line where the error occurred, the overall loop should work for a varied range of Source Workbooks while still maintaining my 501 import limit however, thus far, I've set the limit on the Source data to be read at 3000 lines. I will probably increase that to 5000 pending the largest product file from the factories I'm currently using. I know one is a doozie but, cant remember how many total products currently? Feel free to comment as I'm sure there's much quicker/simpler ways to do what it is I did below?
TIA, khleisure

Code that seems to be working thus far is below and modification of above for what I wanted it to do.

Private Sub ImportExternalDataToOrderForm_Click()
'*******Exit Sub - Used to disable command button till sub written
' Get customer workbook...
Dim customerBook As Workbook
Dim filter As String
Dim caption As String
Dim customerFilename As String
Dim customerWorkbook As Workbook
Dim targetWorkbook As Workbook

 
' Active workbook is the Target Workbook
Set targetWorkbook = Application.ActiveWorkbook
 
' get the customer workbook to use as Source WorkBook
filter = "XLS files (*.xls),*.xls"
caption = "Please Select an input file "
customerFilename = Application.GetOpenFilename(filter, , caption)
 
Set customerWorkbook = Application.Workbooks.Open(customerFilename)
 
' Ranges vary in Source Workbook to Target Workbook but, applicable data to import to Order Form
' Import data from customer(source) to target workbook(active Order Form)
Dim targetSheet As Worksheet
Set targetSheet = targetWorkbook.Worksheets(2)
Dim sourceSheet As Worksheet
Set sourceSheet = customerWorkbook.Worksheets(1)

targetSheet.Range("B4").Value = sourceSheet.Range("C2").Value ' Works Great
targetSheet.Range("B9").Value = sourceSheet.Range("C8").Value ' Works Great
targetSheet.Range("G9").Value = sourceSheet.Range("C9").Value 'Works Great
targetSheet.Range("N4:N6").Value = sourceSheet.Range("N2:N4").Value ' Works Great
targetSheet.Range("J18:J20").Value = sourceSheet.Range("K7:K9").Value ' Works Great

     ' below 2 lines work for fixed range and every line regardless if filtered
     ' and regardless if Order Qty is blank
'targetSheet.Range("A27:A527").Value = sourceSheet.Range("A13:A513").Value
'targetSheet.Range("D27:D527").Value = sourceSheet.Range("M13:M513").Value

'***** LOOP THOUGH PRODUCT AND QTY ORDERED DATA FOR BALANCE OF IMPORT
' Need to Loop through all Rows of overall Source (Starting R#13) to account
' for filtered lines that exist between the lines that remain and have a qty
' in the Order Qty Field (Col M).  If Qty Ordered Blank (filtered) you pass up
' the import of Source A & M to Target A & D and move to next.  If Qty Ordered from
' Source has a Qty entered, you drop through to import accordingly from Source to
' to Target.  Set Currently at Max Source of Range A13:A3000 (Can increase if
' necessary.  Also, counter to limit the number of imports to max 501 per Order
' Form's limit of lines currently.  Have to modify Order Form and loop below if more

Dim t As Long
Dim s As Long
Dim r As Long
'Dim rcount As Long (removed due to error below)
'*****

t = 27 ' Target Starting Row to accept imported data
s = 13 ' Source Starting Row to begin import consideration
r = 13 ' Define Start counter in For/Next below
       ' with Max set to 3000 potential rows currently (can increase if necessary)

'rcount = Workbook(sourceSheet).Cells(RowCount, "a").End(xlUp).Row ' error here
'rcount = customerWorkbook.Worksheets(1).Cells(RowCount, "a").End(xlUp).Row
      'Above Line creates Error 1004 Application-defined or Object-defined Error
      
' For r = r to rcount Step 1 (removed because of above error)

For r = r To 3000 Step 1

    If t <= 527 Then ' 501 max occurrences that can import data "t" starts at 27
    
       If sourceSheet.Range("M" & s).Value = "" Then
       
            If r = 3000 Then
              customerWorkbook.Close
              Exit Sub
            End If
            
         s = s + 1
         
       Else
       
         targetSheet.Range("A" & t).Value = sourceSheet.Range("A" & s).Value
         targetSheet.Range("D" & t).Value = sourceSheet.Range("M" & s).Value
         t = t + 1
         s = s + 1
         
       End If
       
    Else
       customerWorkbook.Close
       Exit Sub
       
    End If
       
Next r
    

' Close customer workbook
customerWorkbook.Close

End Sub