Hi and welcome to the Forum!! This is a question that all of us have had to face and it's an entirely personal one. With what you have said you will use the iPad for well then I think the 16gb one will be enough for you, but having said that once you do get an iPad you will be truly amazed with what it can do for you. There are all the different apps that will surely entice you and before you know it you could have oodles of them. Do you like taking leisurely drives and traveling, there is GPS which I for one use quite frequently, the screen size makes it so easy to view and then there are all the different location maps available for travel. Then also photos, music and movies, of which the iPad is just superb for listening to and viewing these types of entertainment. Some of us use it to run our daily lives and quite frankly put our lives on the iPad. The list really does go on and on for what we can use this wonderful piece of technology for and before you know it you have run out of room and wish you had bought a bigger one. I have seen many posts of just this. If you are good at managing your iPad, you can have apps, music and movies stored on your PC or laptop and just have what you are doing right now on the iPad. That's not me, I got the 64gb 3G, and I am so happy I did. Have at look at all these topics and see what interests you also have a look around the Forum to see what everyone is using theirs for. Hopefully this will make your decision an easier one.
Good luck!!