Neil,
if you have a UK van then it will usually have a battery already.
Reich Movers are probably the most commonly fitted, with Power touch also being a frequent fit. Any mover will require specialist brackets and these two would seem to have them most readily available. You do not need an auto engage, in fact I deliberately steered myself away from one due to cost and I thought it was something else to go wrong.
You can fit yourself, but I'd advise looking up Midland Motor Mover as they are a well used company, with a good track record on Eribas. I think you will realise for what they charge to fit it is not worth the hastle.
Colin