If you prefer a texture with the red beans, the best way is to make the bean paste from scratch, so buy the cooked and seasoned red beans (you can easily find the canned type in Japanese market) and add to the paste.
We do sometimes add the red beans to the sticky rice so the finished up zongzi will have bites of beans in them. In this case, you need to soak the beans in clear water separately overnight.
But I’m not sure if it will produce a good texture if you add the beans in the paste.
You can make red bean paste using this recipe: http://omnivorescookbook.com/recipes/how-to-make-red-bean-paste (before mash the beans, scoop some out and save for later)

If the center of the dumplings have uncooked rice, it’s probably because you needed to boil them more. Due to the size of the dumplings and how tight you wrap them, the cooking time will change. If you wrap the dumplings very tight, it’s also difficult to cook through. Did you cook it on stovetop or an Instant Pot?

Usually the bamboo leaves are not reused. I think you could, but it takes a lot of work to clean them (the sticky rice will leave residual on them), and you’ll need to make sure they are quite intact after all the wrapping and unwrapping. The other thing is, the bamboo leaves will infuse a nice flavor to the rice. I imagine that if you use them, they will be less fragrant because you’ve boiled them for a long time.
If you can find bamboo leaves, they are actually quite affordable and it comes with a giant stack (I usually have a ton of leftover leaves). So I wouldn’t worry too much about reuse them.