Regarding the block heater, I'll defer to EIGHTLUG's experience. However, I did an internet search for "LR4 block heater" and what I found is that lots of used Land Rovers in northern latitudes have them. If you want one, I recommend you get it through the dealer and have them install it.
About that magnetic block heater you referenced: as you mentioned, there's the skid plate under the car to contend with. Also, I think the oil pan is aluminum or other non-ferrous alloy.
As for the Goodyear UltraGrip tires, I can not comment other than to say that they are specified as the approved winter tire in the Owner's Handbook. But I recommend chains no matter what tires you have. There are lots of situations where nothing else will do.
You might also need chains to satisfy regulations. In our local mountains, when the "Chains Required" signs are out, the policy for Land Rovers seems to be you don't have to have your chains mounted, but you do have to have them in the car. It wouldn't surprise me if the same policy was in place in the frozen north.
Land Rover hasn't done us any favors where chains are concerned. The clearance for chains between the tire and suspension is more like it would be for a sports car than an SUV. So we have to be careful which chains we choose. Land Rover has "genuine" chains available. That means, of course, chains that could be had elsewhere under a different brand name for a fraction of the price. I have chains for our LR4. They are
RUD Grip chains in size 0141, which are appropriate for 255/55R19 tires. Land Rover recommends that chains only be used on the front wheels. Common off-road wisdom says that if you have real 4WD you should have 4 chains. I've read articles and posts which describe "Land Rover Experience" instructors using chains
on all four whees. And
where they recommend just using them on the back wheels. I have fitted my chains to both front and rear wheels, but haven't had occasion to drive with them mounted. Having had them mounted in both places and seen the clearances for myself, and in the absence of personal experience, I tend to favor going with chains mounted only on the rear.
If there are those who have used chains extensively, please chime in!