Earning candy by feeding berries to gym defenders

I can answer number 2: I have never hatched/caught any Snorlaxes, and yet I have obtained a Snorlax candy for feeding a Snorlax. So yeah, you can obtain candy for it.

Nah, luck and luck only, no guide available.

Just save all your berries for the species you want candy and look out for their pre evolutions in the same gym or find another gym to feed.

you get 1 or 2 candy for feeding 100 berries. really not worth worrying about it. assume you'll never get 1 and once in a while you'll be surprised. but you have 1 second to see the small animation or you would never know you got one.

Silph road was conducting research on this last autumn but as far as I know they never published anything about it.

1. From personal experience (12k+ fed last time I checked, tracked from 4k to 10k) nothing seems to influence it. It's just completely random.
2. You can. The candy will be there when you get one of that family.
3. Concentrate on the pokemon you want candy for, put them into gyms yourself when you can, feed more and then some more. It's about quantity, not really any strategy behind it.

1) Just a really small random chance with each berry fed to receive a candy. It'll pop up in the top right corner like when you receive candy from catching or transfering a pokemon.

2) Yep. Definitely possible. I've received Heracross and Mr Mime candy, but have not caught them. It will just be held in the aether until you do catch one. Similar to if you were to transfer all of the pokemon of an evolutionary line, you still have the candy but you just can't see it.

3) Just spin lots of stops to get lots of berries, then feed lots of pokemon. To maximize your chances of receiving candy for a specific pokemon, only feed that pokemon. Every berry fed to another pokemon is one less chance to receive candy for the pokemon that you want.

I suspect there might be a correlation between buddy distance and probability for obtaining a candy by feeding. I usually only feed Blissey/Chansey or Dragonite (not Tyranitar which is easily obtainable by duo-raiding), and candy drop is quite rare. In the past I remember feeding Golem when I wanted to find out how I could see the candy drop, and then I received two candies in one round of feeding (10 berries), which I don't think I have seen for Blissey or Dragonite. I stopped feeding Golem of course so I have no systematic observations, but may be others have similar experiences?

Only info I ever read said it's 1 % chance each time, no other factors.