Hi eyeful,
Regarding the surveillance van, there is no perfect vehicle as there is always a trade-off. Where will the majority of your work be? Like belle88 says, if your in the city a white van blends in great, but if you're out bush a ute or 4wd is better suited. Hatchbacks and smaller vehicles are easier to park and are usually quicker off the mark. Vans are great for comfort during long stationary sits. 4wds and vans provide extra height, which gives you a better field of vision, especially in car parks. There are other things to consider like fuel/running costs, diesel vs petrol vs lpg; automatic vs manual transmission; engine size/power etc.
So as you can see it's a case of horses for courses. In a perfect world you would have several vehicles at your disposal to mix and match as the situation warrants. When you get burnt in one car you can let the job cool for a week or two, then go back in the other and don't have to pass the job on to some other poor sucker.
As far as a DSLR, don't over think it! Insurance surveillance is about VIDEO, VIDEO and VIDEO. The majority of modern video cameras have a descent photo mode, and in 99% of cases that will suffice. If you have a DSLR already and want to put it to use, you'll be taking photos of Claimant's cars and their properties. Many DSLRs become dust collectors and added weight to a kit bag. Video stills are captured off the video with your computer or camera and incorporated into the report. Granted, they are not of the quality of a 18Mp DSLR but as they are resized down to around 400x300 with 6 or 8 to an a A4 page, it doesn't make a very big difference in the appearance/quality.
Few investigators these days would bother to stop taking video; put the camera down; pick-up the DSLR; take an ID photo of the Claimant; put the DSLR down; pick up the video camera and continue taking video. That's how we did it 20 years ago. It risks missing some sort of significant movement/activity on video for the sake of an ID shot.
Put your thought and money into your video gear as that will be the equipment you'll use every time you leave home. A DSLR camera comes way down the already long list.
Also CapitalStudent,
Do a medical? Conducting surveillance on the Claimant when he/she attends a scheduled medical appointment. Often in the city CBD.
Leadbootz