I don't see any Stoic practice as problematic or risky, but I would advise to engage in extreme versions of the negative visualization exercise only if you are an advanced practitioner. The negative visualization is a meditation during which you visualize, slowly and deliberately, something bad or discomforting happening to you.

In my mind, there is no reason why Stoicism shouldn't become as popular as Buddhism, especially in the Western world, where the dominant culture, Christianity, itself absorbed a large number of elements from Greco-Roman Stoicism.

"Fate permitting" is a standard Stoic phrase meant to remind ourselves that planning things is up to us, but the ultimate outcomes are not under our control. It helps us to develop an attitude of equanimity toward the universe. We should very much try to change things for the better, that's the whole point of the Stoic discipline of action.

The downside of skepticism: it can easily turn into an arrogant position of a priori rejection of any new phenomenon or idea, a position that is as lacking in critical thinking as the one of the true believer, and that simply does not help either science or the public at large.

... it is because one can build a compelling set of arguments - informed by science and thoroughly compatible with it - that to believe in anything despite the complete lack of evidence is, in fact, irrational.

If a theory purports to explain everything, then it is likely not explaining much at all.

There are clearly people for whom Stoicism immediately "clicks," it comes natural, and others for whom it doesn't. Then again, Stoicism isn't the only positive philosophy of life. Buddhism is an excellent alternative, if it speaks more clearly to one's personality or cultural background.