Edy, For belly wood you want wood with high compression strengths. Many tropical woods have this quality. For backing you want High tensile strength. Bamboo is ideal for this but other tension strong woods work well also. For core wood you want wood that has good shear strengths so it will act as a good gluing medium between the back and belly.
Your design, draw length and draw weight and the availability of appropriate local woods will determine the recipe, number of lams and their thickness.
If you have a wood that is strong in tension and another that is good in compression, pair them up in a all wood backed bow. I use hickory for backings and a 1/8" thick piece is good for a backing strip. For bellies start with about 5/8" thick and reduce it until your tiller is correct and you have achieved the weight you are looking for. If you are using boards for belly wood you may have to add a handle riser and almost any wood will work for this because there are almost no(if any) stresses on the handle riser. Pat