Your driller should have the answers to all these questions. Since he has the experience, he should be able to answer the questions.
I don't see how he was able to get 30 gpm out of a 2 gpm well, unless it was for only a minute or so. If that's the case, he should have pumped it for a much longer time.
You can only add screen if there is vein for the screen. If the vein in 20 feet thick, only 20 feet of screen will produce water.