I'd like to start by addressing some common misconceptions that might be influencing your question.
Firstly quantum mechanics holds at every scale, it is not that quantum mechanics fails at some level, it is just that sometimes its stranger properties are producing very small effects. For instance the de Broglie wavelength of a baseball is quite small, so you'd need a very very very small slit to get diffraction of a baseball and the spacing between the bright fringes and dark fridges would be so small you'd just see a gray smudge even if you did manage it so practically you just don't worry about it.
Secondly, the mass of a black hole is not the sum of the masses of all the things in it. The mass of a black hole is a parameter describing what mass in newtonian gravity it looks like from far away. If you have to press an object hard to compress it, then its mass is going to go up (all that energy from pushing hard went somewhere and it goes somewhere in a way that increases that parameter). But once you get it small enough that it will compress the rest of the way on its own then you can try to steal some of that energy back if you wanted to, maybe even more than you put in. So it's not clear how the mass of the final black hole is related to the mass of the object you started with.
So there isn't an obvious size to aim for, and even if I knew the mass of your object to begin with, I don't know how you made the black hole, so I don't know the mass of the black hole you end up with.
Now to address your question. One way to estimate the quantum properties of a black hole, is to compare the compton wavelength $h/(mc)$ to other lengths. If the compton wavelength $h/(mc)$ is much smaller than the other lengths of interest then quantum affects can often be ignored. For a large everyday mass that length is quite small indeed.
So your black hole probably won't have interesting quantum effects that are easy to detect.