I'd do the rounds of the motorhome dealers just as a tyre kicker - look, ask, never commit. Make notes of what interior features appeal to you, which dont, which ones you cant live with and without. Try renting different styles and see what suits best. I'd also have a good look at used vans as there are some great layouts on vehicles going back to the 70s. Also having a look at used vans will give you an idea as to how well they have been built - formica peeling up, leaking shower etc will all be easy to spot.
I personally cant live with a low ceiling as I'm 6'1" and the thought of bending my neck for 6 months would kill me.
If you are a committed wild camper then there are a few things that wont affect you if you stay on sites - its nice to have 100 litres of water storage. A waste water storage tank so that you dont drop waste where you are camping. External toilet cassette - having a fixed waste dump valve is a real pain if you cant find a drive over toilet disposal, at least with a cassette you can use any public toilet.
Fixed gas tank, lot easier than lugging bottles about. Most European countries have Autogas and its easy to fill up with a set of adaptors. My 20 litre tank lasts about 3 months.
Think about where you want to go touring. If you like driving on small roads in the Alps then its not a great idea to have a 2.5m wide and 10m long motorhome, they are also hard to wild camp discretely. If you prefer a motorway to Spain and then a campsite then big is ok - apart from fuel consumption. Smaller vehicles can get you into some truly amazing country, and you get to wake upto to million dollar views.
If the fitout includes a lot of 240V appliances you are committing yourself to having either a generator,
inverter or staying on powered sites. Roof mounted air conditioners are usually 240V hookup, whilst there are
inverter models they chew through the batteries. Have a look for some air con that is connected to the vehicle unit.
Heating might be as important as air con.
Build quality of the interior - I am always amazed at the number of builders who get away with square corners on panels - rounded and trimmed is always better for safety.
I'm sure someone else will be along to put their point of view as well.