So - standard VRS with DSG/MFSW/Maxidot etc - if wanting to add OEM bluetooth - is this just a 'plug in' with all mikes etc already installed or is it a 'full install' still required....? just unclear as to what bits are already 'on the car' and what's actually missing to make it work...

You'll need a full setup - microphone, loom, controller, etc.

Plenty of threads on here and on My GTI forum about installing Bluetooth.

Try searches for 'rSAP', 'Bluetooth', 'BT' or 'hands free' and you'll find quite a lot to think about.

I have a standard vRS with Maxidot and Bolero. Can I add this http://www.incar-emporium.com/product_info.php?cPath=221_187&products_id=5787&TeKnoID=jmkevgmkusgd8nel4868vhbrs0 and it will work?

I believe so, but note these things:

Please note this unit is only compatible with white dot matrix display (MFA / MFD). Installtion is simply 'plug n play' however so cars require coding for the car to recognise the module.

I make no guarantees that it will provide all functions for your phone though.