Open workbook prompts multiple times - vba

Question

A few times a day I receive a file. I'm trying to automate it as much as possible and one part would include having the macro that lets you select a file to vlookup into (the file name is different every time). My macro runs, but for some reason it prompts you to select your file 3 times. I've tried a few variations on the code, but nothing worked. Does anyone have any insight as to why? It is prompting once when first opening the file, once when filling in the first cell with the formula, and again when the macro fills down column with the vlookup formula. I've pasted the relevant part below:
Dim MyFile As String
MyFile = Application.GetOpenFilename
Set firstWB = ActiveWorkbook
Set mySheet = ActiveSheet
Set wbLookup = Workbooks.Open(MyFile)
firstWB.Activate
mySheet.Range("T2").Select
ActiveCell.FormulaR1C1 = _
"=VLOOKUP(RC[-18],'[wbLookup]tempemail'!R2C2:R123C20,19,0)"
Range("S1").Select
Selection.End(xlDown).Select
ActiveCell.Offset(0, 1).Select
Range(Selection, Selection.End(xlUp)).Select
Selection.FillDown
Columns("t:t").EntireColumn.AutoFit
Columns("T:T").Select
Selection.Copy
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False
Application.CutCopyMode = False
wbLookup.Close False
Range("U1").Select
ActiveCell.FormulaR1C1 = "=NOW()"
Range("U1").Select
Selection.Copy
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False
ActiveSheet.Paste
Application.CutCopyMode = False
Columns("u:u").EntireColumn.AutoFit
End Sub
Thanks!

Answer 1

ActiveCell.FormulaR1C1 = _
"=VLOOKUP(RC[-18],'[wbLookup]tempemail'!R2C2:R123C20,19,0)"
This will not work unless wbLookup is literally the name of your file. Excel sees this and prompts you for the actual name.
ActiveCell.FormulaR1C1 = _
"=VLOOKUP(RC[-18],'[" & wbLookup.Name & "]tempemail'!R2C2:R123C20,19,0)"
might work better
This:
Columns("T:T").Select
Selection.Copy
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False
Application.CutCopyMode = False
...could be replaced by this:
Columns("T:T").Value = Columns("T:T").Value
A lot of selecting/activating is unneeded and is better avoided: How to avoid using Select in Excel VBA