I was helped out by an older guy, who had a lot of knowledge of feet and shoes and running in general. I had to do a few tricks ('Stand on one foot! Now the other!') which told him what kind of support and dampening I would need. He was very careful in selecting the shoes I had to try on. I had one shoe on of one pair, and then he took a look. "Oh no! That will never work, because it's too narrow here! Take it off, away with it!" he said. :)
I had to run a few times to and fro, so that he could see what my running style was and how the shoes reacted/corrected that. In the end, I went with the second pair I tried on (of about seven or eight), of a brand that I had never heard of before. They are incredibly comfortable -- my ankles (which are a weak point of my physique) get lots of support. I also bought a few running socks and a short running tight (I will refrain from posting pictures of that, to protect your sanity).
This morning, I did my first training day. I measured the circumference of the pond out back on the map, and it turned out to be roughly 1 km (and not the 500m I had estimated!). I decided to do 1500 meter (instead of the mile that is originally planned for the first week -- it's another 100 meter from the backdoor to the 'circuit'). Not having precise measurements meant that I had to guesstimate the distances, but a few meters more running or walking shouldn't matter much.
I can't believe how much out of shape I was. After 100 meters of running I sound like a steam engine, and I need the full 200 meters of walking to recover before setting off again. I can feel my ankles right now, but I did some stretching exercises, so I hope it'll be OK.
Fun thing that happened: I had just started out on the first part of walking, when I encountered a lady in a tracksuit running. She greeted me merrily -- I was a fellow runner who was trying to clock in his distance before the next rainshower (which thankfully never came).
It felt good to get off the couch and start doing something. All in all, it took me about an hour. That's certainly manageable. I'm not sure if I will run tomorrow as well (might be better to give my legs a day off to get used to the feeling), but on tuesday and wednesday, I'll be running again!