I have fitted the rear view mirror to mine
I bought a fancy lcd 1 for 30 quid off eBay. I already have the rain sensor etc so it was plug and play.
Someone else cut his bulkhead and fitted a plastic window. You can buy them already done with glass and a mesh grill as factory standard.
Not done the windows on the custom but have on the mk7, it is easy enough to do. You normally have the seam on the inside that you can follow with the cutter. 2 options, drill couple of holes in the corners that are big enough for a jigsaw blade to fit in and use a fine steel toothed blade and go around with that, gold the jigsaw steady though as it can batter the metal making it jagged and the base can knock sh*t out of the panel scratching it. Maybe some tape and sponge or something for protection?
Option 2 is the thin cutting disk, 1mm. These are clean on the straights, a little tricky on the corners. But the flaw in them is that they fling molten steel everywhere so you really need to cover everywhere on the van even the glass etc. You may consider removing the doors away from the van which is good but consider door alignment, maybe get a cd marker pen and draw around the hinges so that you can instantly line then up on refitting.
The rest you should watch YouTube for instructions, you buy a fitting kit which is cleaner, prep m and adhesive etc.