Mutual fund advice

Hi, I am 23, looking to create a long term mutual fund portfolio. For starting I am planning to invest 20-25k a month out of which I am investing 5k per month in S&P 500 Vanguard ETF. I am planning to distribute it like 7k small cap 5k mid cap 3k large cap

But i see flexi cap and multi cap funds too. How should I diversify?