This is what actually people do in day trading. This is a good way to trade. But this is a time consuming technique and never rely on one coin. Divide your investment in various coins. Because there is a high chance that the coin you invested in never recovers and your 3%+ sell order remains as it is.
Yes, you can try manually first, and if it works with the help of a bot later.
IMHO when you pick some winners, dumping them at 3% gain is way too little, and when you pick losers you have to choose between getting stuck bagholding or eat the loss by dumping them a.s.a.p. My personal preference is to stay with a couple of longstanding coins and occasionally play with some very promising coins. But when I want to sell, I look at the chart to try to pick a relatively good price.
