Hey congrats on learning to ride. 100 Kms is great for your first year "in the saddle" so to speak.

I forgot what it was like to learn to get out of the saddle, but it sounds like you've got some good ideas here. I wouldn't discount the idea of trying it on a trainer if you have one. It wont be as natural as doing it on the road but the trainer might give you some confidence with it. Rollers...not so much. Save the rollers idea until you have a few more miles under your belt. Also, I would first try standing up on your pedals without turning them. When you're comfortable standing up, then start with the pedaling motion.

Next lesson: out of the saddle with no hands