There is no ideal or set of numbers to start. Ask your self first if you are ready to enter to the crypto world. If you think that your money is enough to buy altcoins then go. The more you invest of course the more profit that you will receive. On the other hand, if you have let say huge amount then try to invest also to bitcoin which give you very good income at the end. Investing to some altcoins is very risky compared to bitcoin that shows very good reputation this year.