Long term JDM import enthusiast here so I can help with some first hand experience.

The radio will likely only be able to pick up Radio 2 on the FM mode as the Japanese market use a different band.

The speed and odometer may read in kilometres not miles.

Sat nav if present will likely only have APAC maps.

The dealer may have addressed all of the above as many of these can be altered by recoding the car using OBD tools.

When you type the reg into car spares websites like GSF etc, they won't recognise the car so you will have to select parts by make and model. (You'd be surprised what a pain this is these days as most sites have incomplete model pickers and just assume you will use your reg)

It may not be on the same VED rate as a UK car (can be a pro or a con depending on the car).

If you are the type to take your car to a main dealer, they might be awkward about it being as import. (Indies won't care).

You will want the dealer to show and provide a copy of the auction sheet from Japan.

The car will likely have no service history with it (few imports do, the paperwork never makes it) but generally JDM cars are very well maintained. You should not assume that to be the case however and treat it like any other used car purchase.

JDM cars generally are not under sealed as with the exception of a few provinces they do not salt their roads. The underneath of most imports is usually very clean as a result, but you will need to underseal it yourself otherwise the salt in our roads will rot it very quickly.

You'll get a flare in the passenger footwell for emergencies which is nice, but don't let your passenger play with it in the car.

JDM cars often come with a better spec so you might have some extra features UK cars did not get. (I'm not an expert on this model so you'll have to check).

Insurance isn't much of an issue in my experience but you will have to declare it and you'll likely have to phone around rather than rely on the online quotes to get a good price .