Dynamic Range + error message

Been working on the following macro:

Formula:

Sub Macro1()

    Columns("E:E").Select

    Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove

    Columns("D:D").Select

    Selection.TextToColumns Destination:=Range("D1"), DataType:=xlDelimited, _

        TextQualifier:=xlDoubleQuote, ConsecutiveDelimiter:=True, Tab:=False, _

        Semicolon:=False, Comma:=False, Space:=True, Other:=False, FieldInfo _

        :=Array(Array(1, 1), Array(2, 1)), TrailingMinusNumbers:=True

    Range("A2").Select

    ActiveCell.FormulaR1C1 = "=(TEXT(RC[3],""ddmmyy""))+(TEXT(RC[4],""hhmm""))"

    Range("A2").Select

    Selection.AutoFill Destination:=Range("A2:A311")

    Range("A2:A311").Select

    Columns("A:A").Select

    Selection.NumberFormat = "0.00"

    Cells.Select

    ActiveWorkbook.Worksheets("Data").Sort.SortFields.Clear

    ActiveWorkbook.Worksheets("Data").Sort.SortFields.Add Key:=Range("A2:A311") _

        , SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal

    ActiveWorkbook.Worksheets("Data").Sort.SortFields.Add Key:=Range("G2:G311") _

        , SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal

    With ActiveWorkbook.Worksheets("Data").Sort

        .SetRange Range("A1:R311")

        .Header = xlYes

        .MatchCase = False

        .Orientation = xlTopToBottom

        .SortMethod = xlPinYin

        .Apply

    End With

    Range("B:C,F:F,L:R").Select

    Range("L1").Activate

    Selection.Delete Shift:=xlToLeft

    Range("A1").Select

End Sub

Although I've come across two problems which I can't quite solve:

1. The "311" part of the range needs to be dependant on whether there's a data point after that value (i.e. dynamic).

2. As the macro is working, it'll post that a column is being overwritten. This needs to be automatically approved - instead of me clicking "yes" every time

Solutions to the following problems would be massively appreciated

Ty
Mdn