I'm gluten-free, should I avoid rice and legumes?

Title. Also, should I avoid natural peanut butter because peanuts are a legume? How about arrowhead gluten-free, steel-cut oatmeal?

Hell naw, rice was my savior on gluten free. Obviously, rice having high starch content means different people are going to tolerate different amounts in different ways. I can handle small amounts of rice. If I go much over a cup of cooked rice I'll get bloated. Others can tolerate more. You just have to decide for yourself on that aspect, but overall starch is pretty innocuous in terms of allergens. As I mentioned, the only issue with starch is that people break it down at different rates, so if you take in too much you may have the issue of too much getting into the distal intestine, leading to bloat. Also, if you don't have a healthy insulin sensitivity, starch can be bad for blood sugar in large amounts. These are particulars though. To be safe, just keep it to reasonable amounts at a sitting and you should be just fine.

Oats are debatable. A lot of oats still contain gluten, usually the more commercial ones like Quaker. I've used the brand you mentioned while gluten free and not had any issues.

As far as legumes go, its all going to depend on how they are processed. Peanuts won't naturally contain gluten, neither will most legumes. But if they are processed in a factory that also processes wheat, then yes they will. If you aren't true celiac, then its probably not an issue, but if you can get the really clean ones, go for them. With legumes, I'd be more concerned about the lectin content. Lectins are a topic requiring a book, but its well worth your time if you wanna do a bit of research on them. Beans and legumes are the worst offenders, but I think most people would do well to avoid them. Cooking tends to eliminate them, but to what degree we aren't sure, as this depends on cooking temp and cook time. I'd rather just avoid them. I've seen reports that taking an n-acetyl glucosamine supplement alongside lectin foods can reduce the damage, as the glucosamine component of the gut mucosa is what lectins bind to. So the NAG acts like a replacement, keeping lectins from binding to the gut wall.

I just want to know the specifics of my already strict diet. Trying to chisel away the intricacies that might be causing problems. Even going as far to cut out vegetable oil, canola oil, and carrageenan from unflavored almond milks. A lot of research needs to be done.