Hello everyone and thank you for all replies! Sorry for slow response, too much work & kids, no time to play.... but now winter is coming and need to get ready! For the questions, please note I'm not a car expert, and bought this car "ready-built"
Rim size: Not really sure, but the Dick Cepec Fun Country tires are 18.5/44-15LT, and it says approved rim is 15x12JJ. These DC tires are very popular here on Iceland, since they can be deflated alot without breaking, for driving on snow in the winter!
Fuel consumption: ca 1.8 liter per 10 km with mixed driving. Sure not the most fuel-friendly car.... fuel tank is expanded to 120 liter, and it is also an extra 60 liter tank, but this one I have not managed to use yet, maybe something wrong with pumping mechanism.
Gear ratio: (translated from Icelandic so not sure if this gives any meaning): 2:70 ratio splitter, 4:88 drive ratio (in addition to standard Pajero 2H-4H-4HLC-4LLC, it is also an extra low gear range range, selected with a mechanical lever at drivers side of gearbox - really nice to use for crawling when the terrain gets rough!)
Rear locker: Standard Pajero!
Front locker: ARB
Suspension/lift: Not sure about type, but done by one of the local companies who specialize in modifying standard SUVs/Jeeps to lifted monsters.
Intercooler: Is supposed to be a bigger one
Oilcooler: Bigger
Winch: Possible to hook up both at front and rear, also for the electric connection. Winch was missing when I purchased it, but getting a Comeup 9000 now!
Snorkel: Also missing, but getting a Safari one. Decided winch and snorkel was a very good idea after me and a friend had a rather wet rivercrossing....
Diff breather: Was only standard, but after first real trip resulting in white oil/water mess in both diffs ==> will be upgraded now!
Air compressor: Builtin, with outlet under the fuel filler cap. The rims has extra valve so you can easily fill while monitoring pressure with a gauge on the normal valvecap.
Others: Webasto heater, VHF radio, extra lights front and side, extra searchlight with pan/tilt, integrated 220VAC converter. AND: Broken inside door handles on both sides (lots of wind on Iceland!)
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Yeah, driving offroad is illegal on Iceland, due to the very fragile nature, which only has a few months to very slowly recover every (cold) summer. But the island has many tracks in the interior, which is more than enough adrenaline, at least for me

And when the snow falls and the ground is frozen, it seems to be a bit less strict. But this will be my first winter up here, so I will learn as I go. Have signed up with a 4x4 club, looking forward to lots of fun!!
all the best,
Gard