Why couldn't it be "We eat rice"? Is that really necessary to put the article?
Because the Irish sentence has the article. If you are translating from Irish to English, you'd have to include it. And the same reverse. It wouldn't be necessary, but "We eat rice" had a different meaning than "We eat the rice"
As the subject is plural, wouldn't rice also be plural...therefore using "na" and not "an"?
The subject is “we”, and is completely independent of the object “rice”. If the sentence were instead Ithimid an t-úll, would you similarly expect that “the apple” ought to be “the apples”, simply because the subject is plural?
When would you use ithimid an rís as opposed to ithimid rís? Is ithimid rís not gramatically correct?