When we prepare black beans over here, we always start with a sofrito;
fry together a little onion, garlic, bell pepper, mild chile pepper and tomato. Then we add the beans. DRY, not cooked, cover with water and continue cooking until the beans are soft.Salt is added last, although if you were to add cumin, I'd add it to the sofrito to begin with. Just before serving, season with salt, pepper, a tsp of sugar, and abundant chopped cilantro. If you want to add lime juice, add it at this moment.
Since I don't work with anything except metric, I can't help much on the cups/gallons/etc., but from lots of experience working with spices, I can assure you that while 1/2 tsp of cumin, for example, is fine for 1 cup of beans, this formula does not necessarily mean 5 tsps of cumin for 10 cups. Some spices need to be used sparingly , so you may find you need a lot less cumin. I find this very true with turmeric, too. Do what the other posters have advised and add the cumin bit by bit, starting with half the quantity.
tell us how it worked out!