If the pistons are the type that screw back, recommend you get a rewind tool - they look like this:-
Laser 1314 Brake Caliper Piston Re-wind Tool Set: Amazon.co.uk: Car & Motorbike
As long as you get one that will fit your pistons, the cheap ones are as good as any - in the region of ÂŁ10 - ÂŁ15 pounds.
Sometimes the pistons can be turned with cranked long-nosed pliers, but chances are it will take more than that.
If the pistons are the lever back type, then a big screwdriver, or a cranked lever will usually do the job.
Don't forget to keep an eye on the brake master cylinder, as the fluid is going to rise when the pistons go back into the calipers.
Cheap disc pads tend to be an unknown quantity, worst case scenario is that they last half as long as they should do, or screech (which can usually be overcome by using brake grease on the back of the pad if that happens) - if you look around you can probably find one of the big names at a heavily discounted price. Halfords tend to be middle of the road re price and quality.
If you are going to do your own repairs, I really recommend getting a manual - the Haynes manuals are cheap and cheerful, and although some mechanics will sneer at them, they are good value for the money.
If you intend using the jack that came with the van, make sure you have something underneath to catch it should it fall - your spare wheel with the wheel you take off on top, pushed under a solid part of the chassis, will usually be enough to stop getting crushed should the jacking point give out or the jack slip.