The Heat/Spice Level: Thai bird's eye chili is a hot pepper (50,000 - 100,000 Scoville units), jalapeno is a moderate heat pepper (1,000 - 10,000 Scoville units). I like the flavor and heat of the Thai chili but everyone is unique when it comes to heat tolerance so please proceed with caution here. I use gloves when working with Thai chili.
Subs: You can use whatever mushrooms you like but shiitake offers a wonderful chewy texture (it has more density/resilience to it). I like bird's eye chili for Thai inspired dishes whenever I can find it however, jalapeno will work fine. You could also skip the fresh chili/pepper and sub 1 Tbsp (or according to pref) chili garlic sauce (it will create an orangy colored broth).
Color of the Soup: I mention this in the post but the color of this soup will vary depending on the type of broth you use. The veg broth I used had an orange hue that mellowed to a butter yellow with the addition of the coconut milk. Chicken stock is a paler color that will give rise to a winter white broth, reminiscent of the classic Thai dish.
Lemongrass: If it's accessible to you without too much hassle, lemongrass is a beautiful addition to this soup. Trim the top and base of the stalk (using the bottom 4 inches or so) and peel off any dry or tough outer layers. Use a pestle or the side of a large knife to bruise the lemongrass stalk by lightly crushing it. Just leave it behind in the soup while serving (a bit like dried bay leaf, you are using it for its flavor but not eating it in this case).
Amount of Vegetable Broth: The tofu and rice, though cooked, will continue to absorb fluid over time so if you're not eating the soup right after making it, you may want to add additional broth (water or coconut milk) to desired consistency.