Protected Sheet With Timestamps And Locked-after-saving Cells

I have this excel sheet I'm trying to create (to make my life better at work). It's to track credit card refunds. It'll be saved on sharepoint. So my department will fill in the data on the "Ops" side, and then the accounts department will fill in their side. It's very rudimentary, but anything is better than the old, tattered BOOK we are currently using.

So far, I have the user/date/time stamps autofill, when the user fills in "Entered by" or "Recieved by". I have those cells locked so no one can edit it. I have separte passwords for both sides (Ops and Accounts).

What I want now is to be able to:

1. Lock each line once it's been entered and saved. Say my department fills in one entry. We save it. After that, it CANNOT be edited. If there are any changes, I'll put in a remarks column so people can enter stuff.

2. If someone enters the first two columns (Guest name, booking number), then the "Entered by" HAS to be filled, or the workbook cannot be saved.

3. ONLY letters can be used for Guest Name and Entered by. I've tried different things for this. While I've managed to make it work if the user enters a digit first, I can still enter John56, and it'll pass. I need it to only allow letters (and spaces).

4. The "Booking Number" should only allow six digits. No less no more than six digits. It can be 000001 even. But it has to have six. And, obviously, no letters, no spaces.

In the "ThisWorkbook" module, I've got this code:

Code:
Private Sub Workbook_Open()
Dim wSheet As Worksheet
For Each wSheet In Worksheets
wSheet.Protect Password:="hurlEy!", _
UserInterFaceOnly:=True
Next wSheet
End Sub

In the sheet1 module, I've got this code:

Code:
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
On Error GoTo enditall
Application.EnableEvents = False
If Target.Cells.Column = 3 Then
With Target
If .Value "" Then
.Offset(, 1).Value = Environ("username")

[code]....