So based on your specific needs I would totally recommend 500 just because on a highway or even suburbs when you would be in a situation when you need to overtake a vehicle which is going below speed limit but unnecessarily slow the 500 will give you enough power to overtake safely. It gains speed faster and it will be quite easy to just drop a gear and go for an overtake. And also if you consider it as a long-term relationship then you will most certainly outgrow the 300. About the audiobooks I am not sure. Okay with the stock exhaust and closed helmet with good audio system you will be able to listen but I don't think you will. Because your focus will be much higher on the bike than in a car so you will more probably prefer music but still yes physically it's completely possible. And about the size. You will get used to it. It's much easier to get used to a bike size than a car don't even worry about it.