Dears good afternoon

I am trying to improve my formula and get a better result.
May I ask for your help

My formula is the following one (used recorder)

Sub lastone()
'
' lastone Macro
'

'
    Columns("G:G").Select
    Selection.SpecialCells(xlCellTypeBlanks).Select
    Selection.FormulaR1C1 = "=R[1]C"
    ActiveSheet.Range("$G$1:$G$3253").AutoFilter Field:=1, Criteria1:=RGB(192, _
        192, 192), Operator:=xlFilterCellColor
    Selection.ClearContents
    ActiveSheet.Range("$G$1:$G$3253").AutoFilter Field:=1, Criteria1:=Array("0" _
        , "43181", "43226", "43240", "43261", "-43270"), Operator:=xlFilterValues
    Selection.ClearContents
    ActiveSheet.ShowAllData
End Sub
What I am looking for is :
Instead of considering only from G1 to G3253, I want excel to understand (thru Loop ?) that I want to consider till the last row available (it could be 1000 or 3253 or 10000).
Also, I want to consider in my filter (column G), all numbers with more than 3 digitals (43181, 43226, 43240 for example) and 0 too

If someone can help me, once again I will be grateful.

In advance thanks
Regards