Rahjik posted...Or is it going to cause major issues by avoiding the Pyromancer class?
The other thing to mention is that you are also asking about the Pyromancer class. The only difference between any starting class is the starting equipment. All starting equipment for all the classes can be found early in the game if you know where to look.
The Pyromancy Glove the Pyromancer starts with can also be acquired from various sources relatively early in the game as well, and it's not all that powerful in the very beginning either.
You can definitely build any class you want out of any starting class. The only thing that will change is how the first couple of hours are depending on your playstyle.