First MH purchase being considered!

My wife and I are considering buying our first second hand PVC Motorhome and are finding it difficult to decide if particular models are value for money, so we wonder if there are some helpful resources available that we have yet to find.

We are still doing our research but are most likely to go for a PVC, rear lounge, two single beds, up to 6M long, 2.2M wide. Our budget including any kit required to get going will be maximum £35K.

In particular the following information would, we think, be helpful:

1. A website where we can input the MH registration number which would then give a value for good, average, poor conditions based on trade in, private sale or dealer prices?
2. Is VAT charged on total price of a new MH, i.e. total price £50k so divide by 120, multiple by 100 to get ex VAT price £46.6k?
3. If 2 above is correct, then should a less than 1 year old MH, in very good condition be worth £46.6k, less depreciation?
4. Is there somewhere that gives typical depreciation rates for particular makes and models?
5. How can we find out the original price when new?
6. Are there technical changes (Euro 5, 6 engines for example) in recent years that should dictate, budget permitting, that it's better not to buy a MH that is pre a certain year?
7. How much negotiation room is there on screen prices typically?
8. How big an influence on prices does age and mileage have? If a car's average mileage is 12K p.a. what is a MH's average mileage?
9. Presumably condition and equipment levels will have a large influence on prices?
10.Do particular makes and models hold their value better than others, if so which?
11. Is it better to buy a MH made by one of the big name converters say Auto Sleepers, or smaller companies say Wildax or the small local firms say West Country Conversions? Assuming they have a layout etc we like within our budget!

Sorry for all the questions, hopefully someone can help us please!