Is it worth investing in S&P 500 ETF and which tech/energy stocks to watch?

I'm a beginner in investing, currently holding a small portfolio with NVIDIA as my main stock. I'm interested in: S&P 500 ETF Is it worth entering now? Which ETF do you use — VUSA, CSPX, VOO? Do you invest all at once or gradually each month (DCA)? Tech stocks Which ones do you follow besides 'big tech' (Apple, Microsoft, Google)? Does it make sense to enter AI companies now or is it a bubble? Energy stocks Traditional energy (oil/gas) or renewables? Which specific stocks/ETFs do you follow? I u