About going back in time to duplicate money and/or profit from lotteries, banknotes have serial numbers in them so it would be a matter of time before people would pinpoint where they come from (so the MC would have to keep moving to different areas if he were to keep duplicating them), and as for lotteries, the slightest change in events can drastically alter the results, so he wouldn't be able to become the next Biff Tannen (and neither should BT even be able to win through the Sports Almanac). He could instead try to profit from stock market, which would still be time-consuming, or to duplicate raw valuable materials such as gold and diamonds.