The max size depends on the type (DXF code) you put in. You should read the DXF Reference. If you use DXF code for strings, it might be 255 char, but elsewhere in the documentation it claims a rise to 2049 char. DXF code 300-309 can be used for arbitrary text strings, but DXF code 1000 can only contain 255 char. Unless the documentation is not corrected at this point and then 2049 chars are available.
So it is not always neccessary to break strings in chunks.