For the new Radio I would use http://peripheralelectronics.com/ model VWAH Adapter:
You will also need Antenna Adapter like METRA Corp. Metra Electronics Corp. 40-EU55
Installation Kit would depend on how your Kenwood mounts & if you can use the Factory Radio mounts on the Kenwood.
You may also need Metra Electronics Corp. 88-00-9008 VW Pocket
(personally) I like Kenwood. Have been a Kenwood & Alpine Distributor for many years & Kenwood is hands down on Warranty & help.(retail) Alpine has a large following & I would never try to sway a customer from Alpine vs. Kenwood, as Alpine does have some very nice Units