Some Questions About The Steem Platform

I've got a few questions I was hoping someone could help with . . .

1. How long do articles stay editable for? Is it a Steemit limitation or a blockchain thing?

2. How are edits handled in the blockchain - is the original article stored, and the a diff is stored with the edit, or is the whole article stored again each time?

3. How long after an article can an author continue to earn revenue from it? For example if I want to write an article 'Best Restaurants in Miami' and update it as new restaurants open and close, is that a model that is supportable?