if your story is true, I think you have a good strategy by making short-term investments. but not all coins can generate thousands of dollars in a short time (yes ... it all depends on how smart your skills are & also the initial capital) but my advice is better to take both options in both short-term investments and also long-term investments.
Right, combination of both is required to succeed in the market. Trading is not linear process, it is multi-dimensional and requires different trading strategies incorporated as single plan. For some coins, one has to hold position for longer period whereas for some, only 2-3 weeks can generate profits.