Ok, lots of questions, and as I am just planning, unfortunately I have no experience yet. So here comes only what i understood:
1) water table: that is certainly a concern. Where tha water table is high, only unperforated pipes can be used. I read though that perforated pipes are better if applicable. Pipes are usually 4-6 inch (10-15 cm) diameter and run underground 7-13 meters. in bigger greenhouses they run into a bigger manifol, or many bigger ones. In my case, there is no watertable to 10 m at least,as I live on a hilltop, so i will go with a perforated pipe. And no permits are needed here at all.
2) You are right about pipe height: since cold air sinks, there is one pipe that is close to the top of the greenhouse and one close to the floor. this is what I plan, too: one end of the tube near the floor, one at 1,5 meter
3) "Will city water be available? Grid electricity?" Yes, our house is close to the city, so no problem with those
4) Stratification? I really don't know
5) I am digging my hole so I have not taken a temp reading that, but I will. I do have data from around the country though about soil temps at 1,2,3 meter depth and they are pretty similar, so I will likely get no surprises: 1 meter temps are usually 4-6 C in Jan-Feb, and 18-20 in Aug/Sep. That is my planned depth, so I used that in my calculations. I could go deeper if I used a backhoe for digging, but I do it manually now