Most of my backing strips and mid-lams are 1/4" thick. I don't taper them, they're parallel thickness. I usually make the belly wood thickness 1", do the glue-up, then taper the limbs from the center to 1/2" width and 1/2" thickness. Depending on final desired length, these dimensions will give me up to 100#s weight.
I posted a pic of the tip of a tri-lam I made a while back, so you can see the lam thicknesses.