Hi Graham,
Congratulations on your new purchase - I'm sure you'll get as much pleasure out of it as we have got from ours since buying in February.
As to what you'll need, going by your list:
Awning - do you want a full awning or a porch awning? We needed a full awning with annexes (for the extra sleeping capacity) and managed to get a Sunncamp awning thrown in. This is towards the budget end of the market and is, I think, essentially the same as the Dorema awnings and one or two others whose names escape me. It has steel poles, which are heavy but with a confidence-inspiring sturdity and is a bit of a pain to put up - which, I believe all full awnings are.
We have also bought a porch awning (made by Apache - possibly mid-range - more expensive than the full awning), which also has steel poles, but these are partly sprung-loaded and easier to put together. On the whole, though, the Apache doesn't seem much better quality than the Sunncamp. If we're going away for a week or more we don't mind putting up the full awning whereas we bought the porch for weekends away. So, my advice to you (if you are thinking of buying as we did) is to get the quickest, easiest porch you can find for any money! I think a full awning will always take time to erect and there's not much you can do about that but, if you can find a really quick and easy porch you'll find it indispensable - so get a cheap full awning and the best porch!
Battery - We have a 110AH, which is considered big. It will just about last a week if we are very careful and hardly use it. If you are always going to use electric hook-up it doesn't matter too much - you will need an electric hook-up lead (25 metres is usual).
Water Carrier - You will need an Aquaroll (or similar), for your fresh water, of around 40L and a Wastemaster (or similar), for your waste (grey) water. You will also need some piping and probably a Y-piece (available from any caravan accessory shop) to connect your caravan waste outlet to your Wastemaster.
Wheel lock - You'll need one to appease your insurance company at least. Ours is by Milenco who are very well known (though there are others).
Hitch lock - Very useful and your insurer may want one. Ours is by Al-Ko, who made the hitch.
Mirrors - again, Milenco are amongst the most popular with their Aero and Grand Aero designs.
You will also need:
Some gas (propane for all year use), regulator and gas bottle spanner.
Levelling ramp (and chock).
Toilet Chemicals (pink for the flush and blue for the casette).
Corner steady winder.
Step.
If you're getting an awning it's worth splashing out on some decent pegs. We use Tarzan pegs, which are about 9" steel and suitable for any surface.
I think that should just about do you!
Try and get the dealer to throw in as much as possible.