Could I please ask for some advice on DI water and getting to use it with a hose and pressure washer?
I've found canisters on Ebay, not sure what size to go for with respect to resin qty and it's likely life. 11 & 19L seem common.
Also, how have you got this working with a pressure washer? Is there a pressure drop when connecting a DI vessel to the washer?
Which wax do you use? Paintwork looks stunning and the glass (which is something I'm struggling with) looks perfect. Care to share your chosen products??? 
Yes, of course, happy to advise.
DI water filters are very easy to set up with your normal garden hose and a pressure washer. The water filter vessel simply sits between your tap and the hose and your hose connects to your pressure washer as normal. The DI filter needs a short piece of hose leading from the outside tap to the IN source on the top of the vessel and then connect your main hose to the OUT connector. Then connect the main section of hose to the PW. You need a couple of hose end connectors for each section of hose. I have not found any drop in pressure with mine.
The DI filter I use is a Raceglaze 7L but if I was buying again I'd probably get a larger one. Raceglaze ones are quite pricy but very sturdy. You can get less expensive ones on ebay and other places. Usually they come with resin but you will need to replace the resin. How often will depend on what exactly you use the DI filter for. I use it for everything - filling buckets, snow foaming, all jet washing and rinsing, and I refill my resin twice a year on average. I buy mixed bed resin in large quantities from a window cleaning website as it is cheaper from these places. I would also recommend getting a funnel as this makes refilling much easier. Also worth buying a cheap water hardness meter for checking the hardness of the water coming out so you have an idea of when the resin needs replacing although you will be able to tell as you will see water spots on your car.
This is the filter I use.
http://www.raceglaze.co.uk/car-care-exterior/wash/400-litre-0ppm-car-washing-filter/Connectors
http://www.raceglaze.co.uk/hozelock-style-hosepipe-end-connector/
And cheaper resin for refills from these places
http://www.windowcleaningwarehouse.co.uk/unger-resin-25l-bag.htmlhttp://www.cleaningspot.co.uk/cgi-bin/ss000002.pl?SS=mixed+bed+resin&search.x=0&search.y=0&search=ACTION&page=search&PR=-1&TB=A I would highly recommend a DI water filter if you have a mid to dark car and live in a hard water area as it takes the stress out of car washing, especially during the sunnier months, and stops that race to dry the car off before the sun does and dries on the water spots.
Wax I'm using at the moment is Swissvax Crystal Rock, which is a very high carnauba content wax with a hefty price tag, but then I have used many great waxes and am trying out higher end waxes at the moment. Very impressive they are. I buy the smaller sample pots (30ml) which keeps the price manageable.
For glass I use Gtechniq G6 Perfect Glass Cleaner and apply Gtechniq C2v3 on all glass ever month. I'm not a fan of C2v3 on paintwork bur it works very well on glass and also on wheels.
There's a lot of really useful info in the forum detailing section but here's a couple of my threads that might prove useful. I've used a lot of different products on my cars but these threads will give you an idea of my go-to choices. If you have any other questions, feel free to ask.
My first detail of my R
http://www.golfgtiforum.co.uk/index.php?topic=275907.0General detailing advice thread
http://www.golfgtiforum.co.uk/index.php?topic=277318.0
