I've been vaping on-and-off for a couple years now. I started with one of the Njoy 510's bought at a gas station. Went from there to an actual 510 manual, to a Innokin Lea, and finally a few days ago to an Ego-T. I had a lot of problems with juice leaking into the battery on the automatic ones. The Ego is about as big around as a large fountain pen, whereas the 510's are more the size of an actual cigarette. As for flavors, there is about anything out there you would want. I would recommend just trying a few out.
Edit : as for battery life, I would probably go with a larger battery than the 510, or make sure you get a few 510 batteries. Nothing worse than to step out on break for a quick vape, only to find out that your battery is dead.