I think your layout will be determined by the condition of the stave. Go as wide as you can - 1-3/4" or more, if possible. I've been successful with a couple of pyramid ERC layouts that started out around 1-3/4". If you don't have enough width, you could consider an ELB.
4" diameter is not much. The heartwood will meander, and you might have to make a mostly sapwood bow. That'll work, but ideally, you'll have a mostly heartwood bow with a thin layer of sapwood.
You'll likely have some pin knots. That's okay. Just avoid the big ones. Be warned - ERC loves to explode. You'd do well to back it, especially if you don't have much width/length to work with.