initializing char pointers

Yes, it's good idea. Google Code Style recommends:

1. To initialize all your variables even if you don't need them right now.

2. Initialize pointers by NULL, int's by 0 and float's by 0.0 -- just for better readability.

   int i = 0;
   double x = 0.0;
   char* c = NULL;
   

It is good practice to initialize all variables.

You cannot store a string in a pointer.

Your definition of mgt_dev_name is good, but you need to point it somewhere with space for your string. Either malloc() that space or use a previously defined array of characters.

char *mgt_dev_name = NULL;
char data[4200];

/* ... */

mgt_dev_name = data; /* use array */

/* ... */

mgt_dev_name = malloc(4200);
if (mgt_dev_name != NULL) {
    /* use malloc'd space */
    free(mgt_dev_name);
} else {
    /* error: not enough memory */
}

If you're asking whether it's necessary, or whether it's a good idea to initialize the variable to NULL before you set it to something else later on: It's not necessary to initialize it to NULL, it won't make any difference for the functionality of your program.

Note that in programming, it's important to understand every line of code - why it's there and what exactly it's doing. Don't do things without knowing what they mean or without understanding why you're doing them.