Usually the strength comes from the rim and then you need spokes to keep the rim in place I think. 32 should be plenty strong. Strong alu rims for 26ers mtb start at about 500g or so and end at about 700g. For 29er mtb you can add at least 50-100g to that. Strong road rims start at about 500-550 or so think dt tk540.
You also want:
welded rims, not pinned or sleeved.
butted spokes like comps or alpines. Get the known brands.
brass nipples.
double eyelets.
even tension in all spokes. (That you can only get from a round rim to begin with)
And so on...