I think your plan sounds great. I do short goals that I keep in my mind...like "next time I ride a long ride, I want to do 30". I got up to 50 this year but haven't been past it yet.

As far as riding alone goes, it is much easier if you find someone to ride with. I ride alone a lot and that's great for base training. I've found, though, when there is someone to socialize with the time goes by MUCH faster. Same goes for group riding. Before you know it, miles have gone by and you are almost done!!!