Pokemon-go – How does a Pokémon gain CP when evolving

Like Samthere said, you can delay indefinitely, however id recommend keeping one Pokemon high to take gyms with. Don't power it up more than you have to but keep it high enough to get at least a few gyms. The extra star dust and coins you get should be worth the candies and stardust you spend to keep just one Pokemon high. I usually get rid of anything with a CP meter under 90%. It's probably good to set a goal like level 25, otherwise you probably will delay it indefinitely. Lastly, go ahead and evolve any Ratatas and Spearows (or other really common ones in your area) you can for the experience. Their evolved forms max out pretty low so they aren't really viable later, otherwise leveling will get really slow unless you are hatching eggs left and right.

YES.

The number is 1 candy per transfer to the Professor regardless of the position in the evolution chain.

Source: Personal experience. Tested it with exactly your example (pidgey, pidgeotto or pidgeot) and others. And I also tested it with high CP evolutions (e.g. Raticate for which I need 2 candies for Power-Up also gives only 1 candy at transfer.) What isn't secure: A Gyarados - to give an example - might bring more than one as it needs 400 (!) candies to evolve and seems to follow no rule in this regard.