Wow! It sounds like you've got a lot going on. If I were you, I'd just stick to LHTH and the co-op class, without trying to extend the class at home. I'm sure he'll have a lot of fun and will learn a lot in the co-op class, but he's also clearly learning a lot with LHTH, and you're also doing phonics with him, right? So I think he'll be fine with just that.
As far as your other question goes, about books to read to him, what if you just get a couple of the many wonderful children's book treasuries available? Listening to books read out loud is great and will really help prepare him for LHFHG, as I'm sure you know, since you're already doing it with another child.

What we do is we have 3 really good treasuries of stories and one really good children's poem treasury, and we read through a story and a poem each day at the beginning of pre-school time. I just start at the beginning of the book and work my way through. We read a lot anyway, but this is getting them used to listening during school time and it also helps me to make sure them been exposed to a variety of great literature, instead of just their favorites over and over and over.

It sounds like that's kind of what you're wanting, so you might give it a try. If you need some recommendations, pm me and I can let you know what our personal favorites are right now. HTH!