Zamenhof presented the Fundamenta Krestomatio as a model of Eo style (modelo de esperanta stilo). This gives the impression that any Esperantist who wants to write good Eo should read that book. But then, is it preferable to read it quite early (that is, as soon as one has an intermediate level of Eo), or after several years of practice in order to consolidate and purify one's style?
Or is the Fundamenta Krestomatio out of fashion and other Eo works should be prefered as models?
I've been using Esperanto for almost two decades and I have a copy of the Fundamento on my bookshelf. I have never read the Fundamenta Krestomatio. I've seen excerpts from it in my searching through the Tekstaro, but I always try to compare anything I find there with more modern texts if possible.
For a rough answer to the question of what should be used as models, take a look at what texts were included at tekstaro.com .
The Fundamenta Krestomatio is still a model of excellent Esperanto. Few of the expressions in it are archaic. The content isn't modern but that's all. Any Esperanto learner who masters Esperanto to the level presented in the Krestomatio should be very proud of themselves, furthermore no Esperantist who considers themselves expert could criticise you if your language was as good as that found in Krestomatio. As far as when to study it is concerned - as soon as you have a thorough grasp of the grammar and have learned between 1000 and 2000 roots and then any time after that.