I agree that. I think the thing that is necessary is the set of all possible universes. That is necessarily what it is. These universes may exist in actuality as a kind of multiverse but I think it more plausible that they exist only as potentialities in God's mind. God is free to actualize specific universes from this necessary set and I think the ones he chooses to do, which is perhaps only this one, comes from your point that God is love. He would not therefore chose to create a universe where there is so much evil and suffering that goodness couldn't really survive. I believe He chose to create this one because this is a universe in which ultimately good triumphs.
I'm really glad you brought this up. I am of the opinion that modal logic can be such a powerful tool, and is too often underutilized by theologians. In fact, it didn't even occur to me to try and employ it in the context of this question, haha.
So, if I'm tracking what you're saying, the set of all possible worlds are ersatz worlds in God's mind (David Lewis is one of the few philosophers that I'm aware of that holds that the set of all possible worlds are ontologically real). God is free to actualize any of these worlds, or perhaps none of them. I think the possibility that God is free to not create at all is important, otherwise we are back to the notion that God is essentially Creator and some created world must obtain.
If, for the sake of argument, we assume that it is God's essential nature of love that is the impetus for creation, then it makes sense that there will be some worlds that God would not freely choose to create. For instance, a world were evil was so predominate and redemption did not occur would be one such world. Of course, this begs the question as to why create a world with evil at all. But trying to address that would be out of the scope of this thread. We might eliminate other worlds, as well, but I don't think they would be very many. We might eliminate worlds where there are no intelligent creatures who come to know God's love (again assuming that love is the impetus). But, maybe that is assuming too much. I suppose God, out of love, might create a world where no one comes to know and worship God.
I am hesitant to assert that this is the best of all possible worlds, or that the actual world is the only one where ultimately good triumphs. For instance, there is a possible (ersatz) world sufficiently close to this one where everything is exactly the same, except I am wearing a red shirt instead of the grey shirt I am now wearing. In that world (where I am wearing a red shirt), redemption is also possible. That may seem like nitpicking, but it's important because it means that there are many, many worlds that God could have created where good ultimately triumphs. So, God is not constrained to create just one world, but free to create many, in spite of the fact that this is the one that God actually created.