Good for you! I can't imagine how much more difficult it is to learn at 50. When you're a kid you're fearless- not so much when you get older and KNOW things can break.
Definitely practice signaling and steering with one hand for brief moments. Then, once you're completely comfortable on the bike- practice reaching down to your bottle cage to get a drink. I used to ride with a woman who had to stop every time she needed a drink. It took us forever to ride 10 miles and I think it was much less safe stopping every 5 minutes to dismount and mount again than to learn to reach for your bottle- but that's just one girl's opinion.

Are you having a blast on your bike?