I'm not an expert but with my experience, I believe it's better to have 50% of your coins on BTC and ETH and rest 50 on others. On diversifying, you should also consider the nature and network of that coin. Investing a large portion of your money on coins from the same network or on coins that are of same sector would put you in risk. As well, the holding of your coins should also be diversified for earning passive income to safeguarding in wallets and some on centralized exchanges for quick trades and transactions.