We've just purchased a 2.4l Alphard Conversion 2003 with just over 50K on the clock. Very comfortable to drive and the conversion is of a high standard. We went for the Hi- Top roof and not the pop-top just to give us more storage and space.
The convertor handled the registration of the vehicle.
The stereo is in Japanese as its fitted with a Satnav etc which is not compatible in the UK. The front camera tbh is pretty poor, however, no real intention of needing it, the rear is excellent. There may be a few other boxes which were for toll bridges etc, they can be removed, however, they don't take up any space if left.
The odometer will probably need converting to MPH and you will probably need to under seal it as they don't do this in Japan due to the climate.
Our insurance was from Safeguard and was about £360 that was with a £250 excess.
Tax is about £280
We are also using this as an everyday vehicle as our weekly mileage is low.
Servicing and maintenance is pretty standard
We purchased it from Fantastic Campervans in Dairsie Cupar Fife. He has a few ready for conversion and few converted, seem to be becoming popular due to the price and they covert very well.
Haven't found any cons
Good luck with the conversion.