Answer: The so-called red barberry (Berberis thunbergii var. atropurpurea) is actually a group of plants. Depending on which variety you have and whether or not it is a named type or a seedling, it would typically grow between 3 and 6 feet tall and wide. One we commonly see for sale though is "Crimson Pygmy" which is a smaller form and only grows about 2 feet tall and about that wide or a bit wider. In any case, the natural habit of this shrub is dense and twiggy with a naturally regular and rounded shape overall. The berries are bright red and remind me of "redhot" cinnamon candies in the winter, but if you prune them most of the berries will probably be cut off.
These shrubs are deciduous and thorny and thus tend to be a bit of a danger where small children and pets are a concern. For the same reason they make a good barrier hedge. They prefer full sun but will tolerate part shade; in part shade they may be a bit greener rather than red. They need well-drained soil, meaning not soggy, but other than that are not fussy. Depending on the "look" you want your hedge to have you could plant them as far apart as their expected width and let them grow naturally or perhaps half to two thirds that for a more solid effect if you plan to trim it.
Q&A Library Searching Tips