1--there will be an MOT,may be two one with chassis no. only and another with reg no.
2--should have UK V5 log book if it hasnt walk away!!
3--doubtfull you,ll get this, you may get a "Tentative Defunct Registration certificate for Export/Eport certificate" this shows previous owner in Japan( doesnt tell you much just chassis no,type of vehicle etc..)wont tell you how many owners though
4--V5 will only tell how many UK owners inc importer
5-- you dont , look at Jap service history and try and asertain if it is correct..but just go by condition of car, mats seats,pedal rubbers etc..very difficult to even decipher Jap dates as they dont use the same system as us, (dates go from last emporers death or start of reign ??? ) may however have whats called a Bimta certificate that will give you confidence that mileage etc is all as stated... but just use common sense if it looks wrong, it ill be wrong !! bear in mind that in my experience Jap imports are in the main very lightly used and low mileage (coupled with good condition is the norm ) and usually year for year they are generally better in the bodywork dept than their UK counterparts..
6-- HPI is esential as it will show anything amiss in the UK history , outstanding finance ,accident damage , stolen etc, but will not show Jap history , If is has a Bimta cert (as mentioned before ) that will hopefully appease any fears on the Jap side of things... but I think in the Main any imports recently into England are very well vetted before they hit these shores !... hope this helps someway..
I wouldnt get too hung up on asking for loads of paperwork that may not be there ,so long as it is taxed and MOT,d and the V5 is available and your happy with the car go for it, Oh but do an HPI check nice if you get both keys , and original Jap instruction book and service history , you wont be able to make head nor tail of it but looks good when you come to sell again