:::, the answer is always "it depends", but as a general rule of thumb, you want a review article, good textbook, practice guideline, or other secondary source that was published in the last five years (or maybe ten, if there isn't much published on the subject).   
 :::Impact factors are a disputed criterion.  The IF for an important niche journal will be much lower than the IF for an unimportant general journal; similarly, a New Zealand journal like this one will have a lower IF than an otherwise identical American journal. 
 :::Your idea of starting small is often a good one.