It’s lovely to hear that he’s back home with you and acts normal!
String of bead poops is evidence that the bun is ingesting hair, but it’s also of course evidence that the hair is passing through. I think all bun owners see the occasional string of bead poops, but it should not happen every day.
Grass hay has a fiber content of at least 32%, it can be higher (up to 40% or so), but I’ve never seen that declared. All grass hay is good, but if you find a type he seems to like he’ll likely eat more of that type. Switching hays can also encourage hay intake – buns like a bit of variation just as we do.
Water intake is important for digestion too. If he’s getting greens you can serve them freshly rinsed and dripping wet so he gets extra hydration that way.
The fiber content in pellets should be at least 20%. There are brands with even more fiber, for example Oxbow Essentials that has 25%.
Grooming is often a seemingly endless and rather tedious task. If you just brush, there will be lots of loose hairs that don’t come away with the brush. I use a lint roller after brushing. It works for normal-haired buns and recess but not for lionheads and angoras. My bun doesn’t seem to mind the lint roller. I like it because it means less fluff flying around and getting in my nose ?