Need help in in syntax to add formula to an existing formula

Hi

Thanks to all that have helped me from the forum so far. I need a bit more help - I've got:

Option Explicit

Private Sub Worksheet_Change(ByVal Target As Range)

     With Target
        If .Column = 1 Then
            .Offset(, 1) = Now
            .Offset(, 2) = "1"
        Dim Cell As Range
        For Each Cell In Target
            If Cell.Column = 1 Then
                If Application.CountIf(Columns(7), Cell) = 0 Then
                    Cells(Cells.Rows.Count, 7).End(xlUp).Offset(1, 0) = Cell
                    Cells(Cells.Rows.Count, 7).End(xlUp).Offset(0, 1).FormulaR1C1 = "=SUMIF(C[-7],RC[-1],C[-5])"
                End If
            End If
        Next Cell
        End If
     End With
End Sub

In which the second part of the code i.e. from Dim Cell - populates column "G" with the unique user input value from Col "A" and then the total (using the SUMIF) is populated in Col "H" for the corresponding unique value.

The other codes that I have are:

Application.Index(Worksheets("REF PAGE").Range("$K:$K"), WorksheetFunction.Match(Target.Value, Worksheets("REF PAGE").Range("$A:$A"), 0))
Application.Index(Worksheets("REF PAGE").Range("$B:$B"), WorksheetFunction.Match(Target.Value, Worksheets("REF PAGE").Range("$A:$A"), 0))

These drag the values from my reference page, based on my Target.value from Col "A"

So the question is - what is the correct syntax - to combine the formulas to:
populate col "G" and "H" using the Dim Cell, then use the application.index formulas to relate to the unique value in col "G" and populate Col "I" and "J"? Is it just a case of changing "Target.value" in the application codes?

I.E.

Col A - User input
Col B - date of input
Col C - qty of input (defaulted to 1)
Col G - Auto list of unique values of col "A"
Col H - Sumif values
Col I - application to index/match range $K:$K from ref page based on value in Col "G"
Col J - application to index/match range $B:$B from ref page based on value in Col "G"

All help will be much appreciated.