Macro help creating claim numbers in a workorder

Some background in what I am trying to accomplish:

I schedule service appointments for a large shop and create the workorder (with a unique claim number per sheet) for the shop. I only have room for 3-4 items per workorder (in order to leave space for the shop to be able to document their work). I often end up with 10+ workorder pages per service visit (each page requires a unique claim number). Customers schedule several months in advance and frequently add on after initial workorder is created. Also, occasionally someone else in my office needs to create a workorder, so the master file will be accessible through a share folder and needs to recognize saves (claim number creation wise)from different accounts (if that's relevant). I need the overall functionality to be as user friendly as possible.

I found a YouTube tutorial from Mr Excel ("Learn Excel 2010 - "Next Invoice Number": Podcast #1505" ...forum won't allow me to post a link) that is super helpful and gets me close to where I need to be, however, I am working with Claim numbers instead of Invoice numbers. Functionally, I think the macros should be close, but this saves to one specific file path every time, which doesn't work for my application. These are the codes for the specific process in the address above:

Macro #1: Generate the next invoice number

Sub NextInvoice()
Range(“E5”).Value = Range(“E5”).Value + 1
Range(“A20:E39”).ClearContents
End Sub

Macro #2: Save invoice with new name

Sub SaveInvWithNewName()
Dim NewFN As Variant
‘ Copy Invoice to a new workbook
ActiveSheet.Copy
NewFN = “C:aaaInv” & Range(“E5”).Value & “.xlsx”
ActiveWorkbook.SaveAs NewFN, FileFormat:=xlOpenXMLWorkbook
ActiveWorkbook.Close
NextInvoice
End Sub

Again, that functionality is close but not exactly what I need.
Is there a macro option that instead of saving to a designated single file (which I don't have), it will open a file path window to direct it? I.E. Create "Save to..." button
Also is there a secondary macro option that would allow me to "merge" with an existing excel workbook (again with a file path window) and save? I.E. Create "Merge with..." button

I would like the macros to only be enabled in the master file, and be disabled once the file is saved to the secondary location.