The flavor of this is absolutely great. On the question of balance, though... Do bard and rat-a-tat levels stack for determining what bardic music abilities the character gets, or just for the number of daily uses? For instance, would a Bard 10 / Rat-a-tat 8 be able to use Mass Suggestion? If so, I don't see any reason for a bard not to take this class: He would still have all of the abilities of a pure bard of his total level (except for a little less spellcasting), plus some extra abilities usable whenever he's in a city.

Also, any permanent-duration ability that carries no expense can get very powerful, very quickly. Every day that your rat-a-tat has nothing better to do with his music, he's going to animate another item. It won't take too long before he's got every bit of trash in the city serving him. To balance this, you might set some limit on the maximum amount of such items he can have at a time... Perhaps 4 times his class level in hit dice?