3 chucks of wood enough for break in time?

The only bad question is the one that goes unasked
That should be plenty for the break in

3 chunks will be fine. I suggest when you do your first cook start with one chunk so see if it is enough smoke flavor for you. As you use the oven it will get better seasoned and that will help with the wood needed to get a good smoke.

The breakin is essentially taking the shine/reflection off the stainless interior walls.

Think of an old blackened iron skillet.
The more use,the better it performs and you want it black.

You could cook a pork butt in it,as you season it and it would be fine.Everything just gets a little better with each cook.