What poundage and draw length do you want? And how long is your design going to be? That plays into the choice of width. For example, I'd go with 1 1/2" to midlimb on a 66" n/n bow if I wanted anything up to 55lb@28". Maybe 1 5/8" wide for 60lb+.
Less length for a draw under 28", less width for a lower poundage than the examples I mentioned. This will let you have adequate wood to do the job, but not so much that your limbs are very thin which makes the bow hard to tiller (small change in thickness throws things off).
And yes most people chase a heartwood ring. Its a little stronger and a lot more beautiful.