"Rice and curry" undersells what actually arrives at the table. usually one meat or fish curry alongside four or five vegetable dishes, each cooked completely differently, plus sambols on the side.
Start with something forgiving: kottu roti (chopped flatbread stir-fried with egg, vegetables, and your choice of meat) is the closest thing to an easy entry point, and hoppers — bowl-shaped rice-flour pancakes, often with an egg cracked into the centre — are worth ordering for breakfast at least once.
On heat: ask for curries "less spicy" without hesitation, it is a completely normal request and kitchens are used to it. Pol sambol (coconut relish) and dhal are usually milder default sides if a curry does turn out hot.