It's tough, because you're right, Simmons probably won't be ready until November - and even then, what % of his best will you be getting? The tough part is, before the injury, he was probably the best LT prospect.
If Left Tackle wasn't such an obvious and glaring need for *this* year, I'd be all in on taking Simmons only, because picking someone like that at 4, someone who's supposed to be foundational for years to come, would make sense.
I like Conerly more than most, I like Ersery more than most, but the top LT prospect who can play this year, would be Membou in my mind. There's no law that says they can't take two tackles either. They can certainly use two.