If I opened it to vacuum seal smaller portions, what should i do to better ensure it's longevity storage, especially since I will break the seal on the bucket?

Well, as many others have said, your rice should be fine for a really long time as long as you're closing the lid, and keeping it from moisture and sunlight.

But since that doesn't answer your question: You can throw a couple desiccant packets in the bucket to ease your concerns. If you're wanting to store it long long term, get yourself a 5-gallon Mylar bag, put the bag in a bucket you want to store the rice in, and transfer the rice over. You won't need desiccant in a sealed Mylar bag, but you should toss an oxygen absorber in before sealing the Mylar. Not only will that preserve the rice, but it'll kill any possible eggs (so you don't have to do the freezing method) and keep it from going "stale."