Hi Jane - welcome to the world of caravvaning, I am sure that you will enjoy many years of this hobby. There will be downsides but just put it down to experience and that 99% of us have been in the same boat as you sometime in our caravan life. Now for the advice - contact TOWSURE (www. towsure.co.uk) or by mail to Sheffield, Birmingham or Southampton depending where you live and have a look at their very comprhensive catalouge. I am sure that you will find all you want at very competative prices with this company. Be careful mind you can go crazy and buy too much.
You will need a gas bottle(s), the size and type can vary, generally the blue bottle is used, Aquaroll for fresh drinking water, a waste water container, electric hook-up lead, low wattage kettle (why use your own gas if you are going to pay for electric?), cutlery, crockery and a few saucepans/frying pan. You will also need the blue/pink chemicals for the toilet. Instead of using sleeping bags my wife and I use a continental quilt over the seat cushions and another over us for bedclothes. Sleeping bags are very clausterphobic and tight unless you are a midget. If you can buy an empty gas bottle cheap at a car boot sale, waste refuse centre, etc. do so as the initial purchase of a bottle and gas is quite hefty as you are paying a deposit for the bottle. Exchange refill bottles are reasonably cheap afterwards. You will need to steralize the Aquaroll with Milton or similar prior to initial use.
Don't take too much as you could be overloading the van. We take enough food with us for 48 hours as nowadays you are not very far from Tescos, etc. Keep all heavy stuff at low level over the axle.
Take the van empty and go to a public weighbridge. Having determined the true unladen weight of the van you can then calculate the maximum load you can put in the van. Also be careful not to overload the nose weight of the van as you will run with the front of the van low and the rear high which could lead to unsteady towing.
I think I have covered most things so good luck to you and enjoy yourself, we have for 30 odd years.