This code will take care of conditions 1-3.
Private Sub TextBox1_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Dim newString As String

    Rem restrict  non-negative integer entry only
    If Chr(KeyAscii) Like "[!0-9]" Then Beep: KeyAscii = 0
    
    Rem impose maximum value
    With TextBox1
        newString = Left(.Text, .SelStart) & Chr(KeyAscii) & Mid(.Text, .SelStart + .SelLength + 1)
    End With
    
    If 1500 < Val(newString) Then
        MsgBox "maximum value is 1500"
        KeyAscii = 0
    End If
End Sub
I don't understand condition 4. "One of the lines needs to be a matrix"
All user entries into a text box are strings, what strings might be entered as a matri