Hey there,
This is really a question of risk tolerance. That said, we can say that research has shown lump sum investing outperforms averaging in over time. This has been proven by many studies (I'll link to an easy to digest paper by Vanguard at the bottom). That said, it can be overwhelming to invest all at once so DCAing over time is usually what most default to. That said, if you know what stocks you want to buy, then lump sum investing (as mentioned) has historically been the way to go.
As for what to invest in? That is very much a personal choice based on your own investment principles. What I can say, is that when I started invest (25+years ago!) I was all over the map. Tried making a quick buck and it didn't work out. I then switched focus and started to build my foundation. After that, I was much better positioned to experiment with higher-risk growth stocks as I had that base of good, reliable stocks supporting my portfolio. This helped with confidence in the markets and allowed for mistakes - which everyone makes, even the likes of Buffet get it wrong some times.
Link to paper: https://corporate.vanguard.com/content/dam/corp/research/pdf/cost_averaging_invest_now_or_temporarily_hold_your_cash.pdf
Does this help?
Mat