You have to delete them using the spade (with the red handle). Then you can put them in again in the place where you want them, using the hoe (with the green handle). It doesn't cost anything to...
after you place it I don't think you can change it.
You could only plow when your plant(s) or Fruits are done.
Yes, you can. Mouse over the multi tools, the 2nd 1 is the move tool (hand), click on it & you will be able to move anything on your farm.
To get more fertilized crops you will need more neighbours as they are the ones whom come onto your farm and fertilise them and feed you chickens.