well my granpa learned me to cut the potatoe when it was quite big to safe on seed potatoes ('heal' cuts with ashes). I used to 'chuck' them in the planting holes too and they always gave me potatoes, lately I (gently) put them in the planting holes shoots/roses facing up (leaving max 3 strong ones, removing all the rest) - pre-chitting is only relevant on early potatoes (says monty don and I don't argue with him
).
Spacing them is almost as important as all of the above, as important as 'feeding' them. When you space them not wide enough you will get massive foliage but less potatoes (not a problem with the early potatoes since they are best when they are little). Some earth up immediately after planting, I wait until the foliage comes up, that way you can get rid of the unwanted herbs more easy.
You only know for sure when they are ready when you go in, barehand, dig up some of the fruit and if you are content with what you find continue, else patience... flowering is a good milestone before that don't bother to dig...