Hard copies are extremely good to have! Unless you have a really fast computer with multiple monitors set up, you're probably going to save a lot of time using hard copies. Rolling the software dice is useful if you have new players, or just a really chaotic first session. It might not be as fast as hard dice, but it leaves a paper-trail if you ever need to go back and look at something. So how you handle rolls really depends on whether you want to prioritize speed, or record-keeping. Since you said this is both your first session on roll20, and your first game you'll probably just go with real dice. If i understand you correctly, you'll be handling character-creation in-game? You'll probably want to give it at least an hour for that part alone. If you want to see the players roll stats, most are fine with it. Usually I don't care, and they still roll in the chat window. It tends to help the group dynamic when people can all react to crits or crit-fails at the same time. But it doesn't exactly hurt anything when people use real dice. As far as stuff to prepare for, all i can tell you is prepare to feel unprepared. I can all but guarantee that you'll be asked questions you didn't see coming, or questions to which you don't immediately have the answer. And at some point, someone will do something silly, unexpected, or just plain unhelpful. Don't Panic, this is actually the good part. This is where memorable stories come from. Also, most people are really patient and nice to new gm's. Very rarely will you come across someone who's looking to make the situation worse.
