I think break in time depends on the boots you get. Whether or not you heat mold them. I've had shop guys suggest ride the boots a bit before heat molding them. Though didn't ask why. I suppose that if you don't need to need mold them don't. In addition I think that if you get properly fitted boots.
I too, suffer from foot pain. I have gone through more boots than I can count on 2 hands in the past year and a half. I would suggest seeing a podiatrist. Ask if the podiatrist is familiar with snow sports. Not sure where you live, but I found a podiatrist in the Puget Sound that specializes in sports including snow sports. Though I would imagine most podiatrists could help you. He/she would probably be able to help you regardless. A simple consultation was a great help to me.