A lot dependson what you want to do with the array of characters at a later stage. There are many C/C++ functions that are designed to work on a "string" - an array of characters with a byte of 0 as then end marker. However if you only intend to process the data as an array of chars the end marker may be unnecessary.
One thing to bear in mind is that C/C++ doesn't automatically extend character arrays to make more space for a longer "string". This is especially important on the Arduino where SRAM memory space is very limited.
I suggest creating a char array long enough for your longest "string" + 1 extra char for the null terminator. You can easily store shorter strings - that just depends on where the terminator is.
...R