Well first off an Orc isn't really the best choice logic wise and lore wise. Orcs are barbarians, warriors, and in some cases necromancers, but in no way stealthy. They are over 6 foot tall and weigh over 250 pounds easy.
However, as far as actual game mechanics goes, I guess it doesn't matter.
But Assassins usually use light armor, archery, one handed, and stealth. Those are the 4 skills you should focus on. Illusion is good if you want to throw in magic to the mix.
My Dark Elf Assassin uses archery for long ranged kills, and backstab with a dagger for a close up execution. It's quite fun, actually.