Assuming this is an all wood and no glass bow....
Tapers help make the limb bend where you want it to. As a rule of thumb, more taper can be used on a narrow deep limb like a Hill style because you have less width to taper on the edges. And a wider limbed bow like a recurve can use less because you have more width taper.
In my opinion, most bows work better with at least some taper lams in the limbs.
According to Roy :D , you want the thick parallel on the belly and the taper in core so you don't cut thru a glue line(assuming an all wood bow)
I'm not sure what thickness you will need but thinking more than .315, my 62" D/R needs .335" total stack for 40# with glass back and belly and an all wood bow I believe needs a bit more....