As a virtually new rider myself and similar in a lot of respects to what you want to achieve cycling wise, I'm going to throw a curved ball at you. I recently picked up a mid 90's mountain bike for next to nothing. It's in virtually new condition and only required a little fettling to get it to how I want it. There seem to be a lot of people clearing out sheds with a fair number of old, but relatively little used cycles appearing for sale.
My plan is to use that for a while until I know what I want from a cycle and upgrade from there at some point in the future. For now, it's doing everything I want and allowing me to maintain sensible average speeds for my ability. It probably won't be high on anyones list to be stolen either, so there may be a hidden bonus there. If you're cycling for fun and exercise, maybe that's an option for you too? Your local bike shop will appreciate the business to give it a once over for you, set it up correctly and want to look after you ready for when you want to upgrade later.
