Which indicator should a beginner learn first?

Learn to read trends (EMA 50/200) and support/resistance first, then RSI (along with the concept of divergence). Add MACD and Bollinger later after mastering the fundamentals. Deeply learning one indicator is better than superficially knowing many.

Which RSI/MACD/Bollinger settings are best for crypto?

Keep the standard defaults: RSI 14 (you can tighten thresholds to 20/80 for volatile crypto), MACD 12-26-9, Bollinger SMA20 ±2σ. More important than the parameters are the context of application (trend vs. range) and risk management.

Is one indicator enough to trade?

It's enough to start learning, but high-probability signals come from confluence: a minimum of 3 factors from different groups (structure, momentum, volatility/price) all confirming each other. Avoid stacking indicators that measure the same thing.

Is technical analysis effective for crypto?

Yes, because crypto is highly liquid and many traders use the same levels/indicators, giving them a strong 'self-fulfilling' nature. However, crypto is highly volatile and news-driven — TA must be paired with strict risk management and no excessive leverage.