Locate 1st Blank Or Last Used Cell In Column

Here is the sheet where I entry new data. From left to right: Productnumber/article/supplier/price per item/starting nr of articles/order threshold/ date 1st order/date of delivery. When I press the button "verwerk" the data will be transported to the sheet "Voorraad verloop" shown underneath. As you can see the first problem consists of the placement of the first table. I can't get it to the first column. The second problem is that when I enter a new product like in the first image, it overwrites the current data in the sheet "voorraadverloop". See the image below. I used the following macro:

Private Sub CommandButtonVerwerknieuw_Click()
Dim iLC As Integer
Dim FindString As String
Dim rng As Range
Dim Lr As Long
If Application.WorksheetFunction. CountA(Range("A4:F4")) < 6 Then
MsgBox ("Niet volledig ingevuld"): Exit Sub
End If
FindString = Range("A4")
If Trim(FindString) <> "" Then
With Sheets("Voorraadscherm").Range("A29:A65536")
Set rng = . Find(What:=FindString, _
After:=.Cells(.Cells.Count), _
LookIn:=xlValues, _
lookat:=xlWhole, _ .................