

Usually red kidney beans (canned), and/or dried lentils in a bag. No prep necessary (besides cutting up veggies) as long as you know there will be enough time for the dried lentils or other ingredients to soften in the slow cooker. I like to leave it on low heat all day or all night to be sure. You could boil/pre-cook them if you needed it to be ready in only a few hours, though.
Nope. If they are given about 3 hours to cook, I find they are softened enough (use higher heat if the duration will be shorter). That’s not to say you can’t pre-fry them or something if you want to!
I should have mentioned that I usually make my chili vegetarian. In the rare occasions where I do add meat, I will pre-cook that, but it’s mostly because of paranoia and because I don’t own a cooking thermometer.