1) What is the best pattern for planting crops? I've been given five carrots by a friendly neighbour of mine, and these things look set to take over the place.

4X6 plot pattern is the one I'm using now, as it seems manageable and tidy (see screenshot). Not sure about how effective it is space-wise or in mass farming.
2) Linked to the 1st one: is cross-pollination implemented in game? I'm looking for any sort of dependency between plot sizes and increasing quality of seeds

3) I've dug a bunch of wells and it looks like there is underground vein or a lake - if you put all wells on a map, there is like a circle underground, with quality increasing towards the center.
Dowsing rod, however, cannot find any well digging spots where the "center" is. If I just build a well on an empty spot, will it still connect to the same body of water?