Personally, and in light of all the post-TOS Trek that indicates that warp is a common skill in the universe and Cochrane only invented warp fro Earth, I find it undesirable to think that there is any trick to warp 2, 3 or 4 after one discovers the basic secret of the drive. It would only be a matter of improvements to the details of the drive, all of them available in the open market, but their integration into a working whole a process that may be beyond a primitive newcomer.
Also, the effect of the chi factor should not be particularly pronounced, or else our heroes should spend much, much more screen time searching for the ideal weather conditions or routes or whatnot. But certainly a degree of chi (mostly time-dependent, thus as much analogous to weather as possible) would make lots of dramatic sense. And perhaps some systems like Sol are especially chi-hostile, with foul subspace weather most of the time, explaining how even ships in extreme emergency haste slow to sublight there.
As for ion storms, steering around them was not an issue in "Court Martial". Rather, it appeared that Kirk had standing orders to ENTER storms whenever possible, to make observations. In "Catwalk", OTOH, it appeared that these storms are massive phenomena that cannot be evaded and will affect even standstill vessels. It doesn't seem there would be any phenomena that only manifest at warp (indeed, our heroes often insist that NO phenomena do, against all evidence). Then again, many of these weird phenomena may well be related to subspace, and are not easily observable by standard physics but will affect subspace technology very adversely, hence the caution and alarm of our heroes.