My $0.02 I would have the basic rosotto nearly done and then add your pan-cooked mushrooms and boiled lobster near the end of cook time. And make sure the shrooms and lobster are still hot, so timing would be crucial.
Not sure if anyone wants to chime in on whether to use parmesan or a cheese in it, like you do with regular risotto, since it's got lobster. You know the Italian tradition and all, the cheese taste overpowers the delicate lobster taste...yada yada. Or does that only apply to fish? I say go with what tastes good, but it depends who's going to eat it I guess!