for ambient temps? an ambient temperature gradient is not necessary. i keep my ambient temps around 77-79° throughout the enclosure (i try to keep it around 80° but it's winter). as long as your ambient temps don't drop below 75° the snake will be fine.
you're not wrong: the UTH is to maintain constant belly heat for regulation, bulbs/CHE help bump up ambient temperatures so it's not too cold.
i addressed the ambient gradient above
100% correct and i would recommend the CHE (though i don't use one).
temps guns will give you peace of mind in knowing exactly what's going on; definitely grab one.
you're almost to perfection! woo!!!