Choosing less coins for holding may more risky or may more wisely. We can not know that actually. Because for example you can choose one altcoin and you can go all in that. and it can do 300x. But you may choose 10 altcoin and you can divide your money to these 10 piece of altcoins and these altcoins may do only average 20x .. So in my opinion choosing 3 or 4 coin is the best number for holding.