Let's start at the beginning, when to prune and feed. You can prune any time you want, no difference really. Feed only when the plant is growing during the spring/summer, very little water and no food during winter. As fert I just use 1/4 strength houseplant fert every couple of months. I've seen cacti/succulent food at the store (1-1-1), but i've never bothered with it. Cacti and succulents don't seem to like a lot of food. As for how much cutting the plant can take, there isn't really a limit so long as you leave enough plant to survive.

I have heard to leave atleast 1/3 of the original foliage.

I have seen them cut back from a 2 ft plant to withing 2 inches of the soil. They will come back. I have one that is in a shallow clay pot. It was only about six inches tall with one main stalk that branchd into three at the top third. I cut all of the foliage off and cut each branch to where only the old tan bark was visible. That was two weeks ago and the plant that had no leaves now has at least 8 new leaves on each branch. Do a search on "whacking" jade or pruning. You will see the pictures of the ones Denise in Omaha cut back all the way to a stump. I believe she has before and after pics. It is amzing. It really helps fatten the trunk as well.