The most persuasive Alphard info source I've found is here:
Toyota Alphard Review - Andrew's Japanese Cars
It seems the typical UK owner's mpg is 25 for the V6 3 litre, 5 mpg more for the 2.4 litre and another 5 for the 2.4l hybrid. Not great, but it weighs 2 tons and has poor aerodynamics.
4WD is an option with the hybrid. It's normally front wheel drive and has Toyota's 'E-Four' gubbins which apparently monitors brake pressure and switches on the rear wheel drive automatically. (Presumably it monitors other things too?) I don't know whether you can select 4WD manually. The rear wheels are driven by one of the electric motors, so you don't get the weight and drag penalty you'd have from the transfer case and driveshaft of a non-hybrid 4WD.
The 1st gen hybrid, the AH10, was thought of as unreliable (for a Toyota) in Japan. The 2nd gen AH20, from May 2008, was OK.
LPG conversion is popular. Supposedly it takes about 30,000 miles to pay for itself. You don't lose any space because the tank goes underneath.
The stereo head unit has to be replaced if you want a radio with British frequencies.
An English translation of the paper manual costs £20.