Would you consider to DCA in S&P500 & Nasdaq100 & Russell2000 simultaneously or just in one index?

I want to build a longtermin portfolio (>5-10years) with index funds based on US stocks.

So the most common are the S&P,Nasdaq and maybe the R2K.

Would you consider splitting my cash in these 3 ETFs? Like 60%S&P, 20%Nasdaq,20%R2K.

Or do you think I should just go with 100%S&P and Ill be fine?

Warren Buffett thinks the average investor should just buy and hold the S&P 500.

Thanks for all of your input!