Importing is straight forward enough if you get someone to do it for you, and I'd highly recommend that. Doing it yourself will end in tears unless you have connections overseas (or can speak/read/write Japanese) I had a company do mine. They sourced the car, got it at auction, shipped it, converted to UK spec (MPH conversion & fog lights etc) and registered it all for me. All I had to do was provide insurance details to the company, pay for it, and pick it up (after a 3 month shipping and conversion wait).
If you do decide to go UK spec then you'll get bigger injectors and brakes, and steel turbo internals as opposed to ceramic jap ones. Search on here for all the differences like quicker spool on ceramic but lower boost limit (from ceramic and injector limits).
If you plan to go single then none of that makes much of a difference, but if you plan to stay with the stock twins, then UK is slightly better in the long run as they handle more abuse being steel and all.