Variable Worksheet Name - vba

Question

I have a macro programme to do some operations like Vlookup, deleting columns etc. The file to be updated would have a few worksheets in it and every time the worksheets' name and order may be different. Thus, I would like to be able to choose the worksheet I want every time I use the macro. However, I haven't be successful.....
This is the macro. I wanted the mySheet to be variable. Ideally, It can prompt me to choose the worksheet I want within that wbSource..However, I have been getting errors. Anyone know how do I do it?
Thanks in advance!
Sub Macro1()
Dim file1 As String
Dim file2 As String
Dim wbSource As Workbook
Dim wbLookup As Workbook
Dim startRange As Range
Dim mySheet As Worksheet
Dim col As Range
Dim Del As Range
file1 = Application.GetOpenFilename(Title:="Select the file to update")
If Len(Dir(file1)) = 0 Then Exit Sub
file2 = Application.GetOpenFilename(Title:="Select the LOOKUP file")
If Len(Dir(file2)) = 0 Then Exit Sub
Set wbLookup = Workbooks.Open(file2)
Set wbSource = Workbooks.Open(file1)
Set mySheet = wbSource.Sheets(ActiveSheet.Name)
On Error Resume Next
Application.DisplayAlerts = False
Set col = Application.InputBox _
(Prompt:="Select Column.", _
Title:="Where do you want to insert the columns?", Type:=8)
On Error GoTo 0
Application.DisplayAlerts = True
col.Resize(, 5).EntireColumn.Insert
On Error Resume Next
Application.DisplayAlerts = False
Set Del = Application.InputBox _
(Prompt:="Select Column.", _
Title:="Which column to delimit?", Type:=8)
On Error GoTo 0
Application.DisplayAlerts = True
Del.EntireColumn.Select '** ERROR HERE!!
Selection.TextToColumns _
Destination:=Del, _
DataType:=xlDelimited, _
TextQualifier:=xlDoubleQuote, _
ConsecutiveDelimiter:=False, _
Tab:=False, _
Semicolon:=False, _
Comma:=False, _
Space:=False, _
Other:=True, _
OtherChar:="-"
Del.Offset(0, 2).Delete
Del.Offset(0, 1).Delete
On Error Resume Next
Set startRange = Application.InputBox("Select the first cell for the formula", "Autofill VLOOKUP", Type:=8)
On Error GoTo 0
If Not startRange Is Nothing Then
Application.Goto startRange
startRange.FormulaR1C1 = "=VLOOKUP('[" & wbSource.Name & "]" & mySheet.Name & "'!RC[-1],'[" & wbLookup.Name & "]NON SLL'!C1:C3,3,FALSE)"
End If
End Sub

Answer 1

Some continuation from comments and possible explanation of problems...
Your code isn't making any errors. However, there could be some logic mistakes which you should consider. This line of code:
Set wbSource = Workbooks.Open(file1)
activate the workbook just opened (file1). And next line:
Set mySheet = wbSource.Sheets(ActiveSheet.Name)
set variable to sheet in just opened workbook (file1) and sheet which is currently active there.
And general question- is this correct for the logic of further part of your code?