Welcome to the fun side!
I think you have great ideas and will have a wonderful time, once you are up and riding.
When I needed a bike with limited funds, I went to my local bike shop, introduced myself and made friends with the crew. I explained what my actual budget was, and they helped me find a used bike, then rehab it. They don't happen to sell used bikes, but they know who wants to upgrade, and were able to point me in good directions.
The local bike shop ( LBS ) was comfortable with me getting a bike that did not make them money right off the bat, because they knew I would need parts, service, a helmet, and all of those other things. They also like my cookie bribes! Their advice was indispensable, from what size to look for to how to pass cars safely.
Remember, you don't need to do *everything* right off the bat. Have fun, and I hope to see you on the road!
I ride my bicycle to ride my bicycle