My recommendation would be to go with the highest payload possible.
When we were first looking at buying a MH the payload was way down on our priorities but luckily we actually bought one with over 500 kilo of excess and we were able to put everything we needed, and more, in the MH without worrying.
Some MHs are very close to being overloaded, dangerous and illegal, even before starting to add all the 'essentials' for going on holiday.
Whichever MH you decide to buy make sure you take it to a weighbridge and find out its real weight and don't just rely on what the Dealer/Salesperson tells you.
It only costs around a fiver, ten pounds maximum, to get peace of mind and to be certain you can actually take items you require.
We've just bought another MH with an excess of 420 kilo and that should be well within our needs.
Remember that buying and transporting bottles/cartons of wine back from holiday will take quite a bit of space and weight, ours certainly do, and we took that into consideration when buying.
The width of a MH doesn't seem to bother most people once you start to drive one.
You just give other traffic a wider berth when you pass them and start to judge whether you can get through a gap with a bit more thought but we've found few problems driving our 7m long and 2.3m wide MH anywhere in the UK and in France.
What you have to worry about when driving is the height of your vehicle and know exactly what you can, and can't, get under.
As for ferries – we've only been on one - Pointe de Grave to Royan - http://youtu.be/xDfUA0zO6b8
They charged a flat rate whatever the length of the Motorhome and probably most other ferries do unless you drive a 'battle bus' or pull a trailer or toad.
Hope this helps.

Au contraire, I would not go with the highest payload possible. It really depends on what you plan to do with it.

If you are going full time, then go big as you can, bearing in mind that for instance a big Winnebago does less than 10 miles to the US gallon, which is maybe fine if 'gas' [meaning petrol] is 50c a gallon. On the other hand, if you are paying £1.30 upwards a litre for diesel, every kilo has to justify its cost. If you have an MH with a big payload (capacity), you'll only fill it up!

If you are going to stay in the UK where you will practically get an ASBO if you dare to park up overnight anywhere except a formal camp site, then why carry the overhead of a shower and toilet? Get a VW bus - a T2 splitty if your are nostalgic and have strong arms, otherwise and more practically, get a modern T5 conversion. [Actually new 'Dubs' have got v expensive, so I mean 'or equivalent' about 5 metres long]. And your juice costs will be (relatively) low. There is a great deal to be said for choosing this as your first van - it'll teach you to be v disciplined about what you carry.

If going continental, then there are stop-over areas ('aires' - see this website) - private and public - where you can take on water and dump waste, which positively welcome motor-homers. Then you do need your own shower and toilet, even if you do pull into a formal camp-site every now and then, but you'll save a lot by using aires. If you plan on long distances, then look hard at getting an LPG conversion. [Remember no Calor gas cylinders outside UK and Ireland, so has your gas bottle enclosure got room for a converter?]

How many people? If more than two, you need driving seats as well as beds.

:thumbs: How long is a piece of string? or would you ask a man that owned a Rolls Royce what it did to the gallon?
The size problem wills always be what the pocket can afford, if you want comfort, storage and the freedom to be able to stop at unsupported destinations or sites. I have a 07 Kontiki645, 7.9 with bike rack, 3.01 to the hump on its back and I have never found it to be a problem. If we keep her down to just under the 60 mph we get 24-25 mpg and that's with a 3ltr under the hood. 21 mph if we attach our trailer carrying a Panda. Weight is the key as too much has the potential to kill not only yourselves but other s near or on the road. Get stopped in France over weight and be ready to pay anywhere around 700 euros. In the UK, fines, points and the prospect of having to leave all over weight goods on the side of the road if you want to continue the trip. Check your own body weights as most as most manufacturers put the driver and passengers weight in at 75 kilo each. Be honest how many of us are there or below. They then state 85 or 90% fuel load. So who sets out on a long haul without a full tank? Of cause set belts are needed if your motor home was registered after Aug 07 so you will need to factor in the added bodies and subtract from the payload allowed. It reminds me of load/weight checking before going flying.
No doubt there are many other factors governing size and weight, but at the end of the day what do you want to do with the 'wheels' and what do you want to do when you get there or do whilst on the way to get there?
We have never regretted our 4.25 ton home from home and that is the main point.
Safe journey's and lots of them.
regards.
Kontki 645.
(Hastings)

All said already is good advice. You need to work out what you want to do with your motorhome, understand the issues involved with each of the parameters, then the decision is solely about what suits you - that is why there are motorhomes ranging from van conversions to Concordes and every size and layout in between.

Not much mention has been made of the significance of length. Over 6 meters you will pay more on most ferries. Last year we went to Norway, paying more for the ferry to Esgjerg and at least double (we are 7.8 metres including the bikes) on every ferry crossing the fjords going up the coast of Norway. But we wouldn't want a smaller motorhome just to save a couple of hundred quid on a special trip like that - consider what you have paid for the motorhome in the first place. With fre or cheap aires or wildcamping available in most countries, ferry cost should be viewed in perspective with the whole package if you intend to travel abroad.

Fuel consumption will be influenced as much by how modern the engine is as it will be by weight, within 500kg or so. other than taht, generally a van conversion with be better than a low-line coachbuilt which will be better than a hi-line coachbuilt, but again, it's all got be viewed as part of the package.

One final issue with weight is that you will only have a licence to drive over 3500kg if you passed your car driving test before 1996, after that and you would need to take a test to get a C1 licence.

Good luck with your search; make sure you visit lots of showrooms/shows. talk to people you meet there about layouts etc, why they like, or have decided to change theirs, then make your mind up and go for it. In relation to spending money, what you spend travelling for your research will be well invested if you end up with the van you want first time - not everyone does!!

The important thing is to understand what willbest meet your needs, plans, dreams and budgets, but remember that there will always be compromises - even if you have £250k to spend, you can't have everything - the benefiits of the layout you choose can't have the benefits of some other layouts, and whatevr you buy is a fixed size with limited space!