A potential user/member registers on the site, providing various items of information. The users are responding to a advert in a publication and the add contains a pin number to be entered as part of registration.

Standard CB with a new field created in Field Management for them to provide the PIN would be recommended. Lets call this PIN field "cb_mypin" for future reference.

Once registered, the user is assigned to a core group member/moderator. The moderator is identified by the pin number.

This is where it gets tricky, CB has no user moderator assignment. All moderators can edit/manage all users. Here's what I recommend to achieve this. You'll need a few incubator projects guaranteed though.

First you need CB Query Field. Once installed you need to create a query to find the email address of the moderator who is assigned the PIN number the user provided. This can be done with the below quite easily. The only tricky part is to ensure the moderator and the user have the same PIN so they'll have something in common. Lets call this query field "cb_mymod" for future reference.

You'll want this field to be hidden so place it on a tab in a not shown on profile position (you still need the field accessible as you need the results). Then using CB Privacy set it not to have an Edit Profile display.

Now that we've a way to match the moderator to the user based off pin we can use this later. The reason we're selecting email address is we want this for later for the emailing.

A welcome message is sent to the new user, in the name of this moderator

For this you'll need CB Emails. Once installed you'll need to setup an email to send after the registration trigger. For the TO address you'd have [email] and for the FROM address you'd have [cb:userfield field="cb_mymod" /]. You'll also want to create a conditional for the mymod field to ensure it is NOT empty as CB Emails will fall back until it finds an email address it can use for FROM (first checks CB registration email, then to Joomlas). You would now have a Welcome email from the users moderator. You may want to specify the FROM NAME as "Moderator" or something of the sort, your choice as we don't have the moderators name, just their email.

At the same time, a message is sent to the moderator to infom him/her that a new member has registered. The details of the new member are also inluded in the message as an attachment in the form of a .vcf file so that it can be added to their personal contact database.

Just do the same as the above but with the reverse (mymod as TO and email as FROM).

In a ddition, moderators should be able to access their list of members and use that to e.g. create a mass mail or send them a newsletter. A total list of all members should also be available, for similar reasons.

Userlists is quite doable, you'd just filter a list by the field created earlier. Mass mailer on the other hand CB can't do unless you do this from backend user management.

The only thing that I am really unsure about, is the creation of a .vcf file with the contact details.

No idea what a VCF file is or how you'd go about obtaining them regarding CB.

iamalive wrote: A .vcf file is an address card file which can be read, for example, by Outlook and other contact management software. Some info is available here: Wikipedia VCard

As this is a primary requirement for my client, I'd appreciate help with this.

I see, CB has no such feature. You may want to check Joomla.org for some sort of extension that could provide them.

We don't do contract development. Please post your request on sites like Joomlancers. I highly recommend checking Joomla.org first as there's very likely a Contact extension that already provides this.