Are there other predominantly tangy/sour spices, similar to sumac? I'm thinking of things for dressing roasted vegetables, where you might use something like lemon juice, but a dry spice can be more convenient.
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
Amchoor (mango powder), anardana (dried pomegranate), and, if you include pastes, tamarinde come to mind.
They all have a tangy/sour taste, and are used quite often in Indian curries, and cooking in other parts of (South East) Asia.
Apart from mango powder (which is rich in citric acid, I use it as a replacement for lemon when I want sour, but no additional juices), I don't have any experience using them outside the realm of curries, so you'll have to experiment your way through them ;)