There is a hive of information on the internet about these buses, below is a collection of links to places I have found useful since owning the bus and hopefully you will find them useful too.
The VW T4 forum – Everything you will ever need to know about your T4 will be here
VW Heritage – Extensive parts supplier to VW enthusiasts
Just Kampers – Excellent parts supplier with excellent service and delivery too!
Mayday Auto Center – Professional, honest, knowledgeable and competitively priced mechanics in Croydon, they work on most vehicles including T4s – just ask for Wayne
Travelvolts – T4 electrical specialists
Brentacre – Comprehensive campervan specific insurance
Motorcaravan – Full guide to re-register your T4 as a motor caravan, worth doing!
Car Mend – Sorted all the bodywork on our van, excellent workmanship and fair price
Wild about Scotland – All things scottish with a camper van twist
Car Gas Struts – Upgrade your tailgate struts