Can we see the entire sketch? Everything, not just the part that you think is having problems?
I mean strcpy followed by four strcats works just fine as long as the array is large enough. Yon't need to assign '\0' to the first char of the array but it doesn't hurt.
Assigning '\0' to the first char of the array and then doing five strcats works just fine as long as the array is large enough.
You appear to have a global array that is large enough, but since it doesn't work for you, something else must be going on. Really.
Show us everything.
Regards,
Dave