Being from Charleston, I know that the north area has been known as the high-crime section of the city for quite sometime. If you live closer to Summerville, Goose Creek, and even West Ashley, you'll be OK. Personally, I would like the cities of Chas and N. Chas to merge into one city of Chas, and if this occurred, I believe that crime would be cutdown, since the city of Chas has one of the best police departments. I know, that's another matter.
I would wait about 5-10 years before moving into sections of Park Circle and lower sections of the city towards "the Neck". When Magnolia and Noisette complete their massive revitalization projects, these areas will be attractive places to relocate.