If you want the butcher block look, you will have to have the 1.5" edge on top. I won't repeat removing the rounded edges, as that has been suggested a few times already.
I will say that wider boards, like 2x6, or 2x8 usually are more select than 2x4's. If you orient the wide face for the top, you don't need too many. If you buy 10' lengths you'll get two per length.
IMO, whichever way you orient the lumber, i.e., on edge or flat, and try to do a glue up with all thread, it won't work like using clamps and cauls. I know because I've tried to do it that way. By the time you drill all the holes, get the glue applied, get the rod in, washers, and nuts, and start to tighten them up, your glue will start to kick. You may not have enough time to line everything up, as the nuts on the thread don't turn that fast.