I opted for the latter however this turned out to require some esoteric knowledge which took me several hours to acquire and learn.
For starters, you need to create custom fields in you Outlook Contacts for info like Account Number and Account Type. There are a number of ways to do this which are easy. Follow the steps here to create your custom fields but ignore the rest of the info on mail merging as it’s useless:
Next you need to create your mail merge template. The mistake I made was trying to create this starting in word. THIS WILL NOT WORK!!! You have to use the mail merge function in Outlook. Select Tools / Mail Merge… and you are on your way. If you start in Word, your custom fields will not appear nomatter what you do to associate them with the contacts folder. Starting from Outlook will guarantee to get you there.
After that it’s a piece of cake. Save your template and any time you want to access it, start all over from Outlook’s mail merge function and open your template from there. If you simply open it from Explorer or Word, you will not have the updated contact info as the template does not access the Outlook Contacts directly. It uses a file containing a dump of the data which is created each time mail merge is run.
So having worked all this out, I now just need to start filling in the contact details. I have set up a separate contacts folder for this as the bulk of my contact names don’t need a snail mail notice each time I move.