It's useless to learn many indicators but you don't use them. I prefer to learn some indicators which is needed
only than spending too much time to learn too many indicators which is not used. Besides, indicators is only tool
and it won't determine the result of trading.
I think, it's a good idea to trade using a couple of indicators which your system is based on.so more indicators you study more better info you get , but you dont have to know all of them to start trading. I can suggest you to use two indicators.
i have a great experience with scalping,macd and rsi indicators.those are greats and specially rsi.so its good for traders to study about indicators for trading.
you can limit your study and application of technical indicators to three for maximum concentration and application,if you rely on more than these it could be confusing and distracting