The ideal initial amount is 0 (zero), you earn some coins in airdrops, giveaways or doing some simple tasks online and then you build your portfolio from there.
That's how you really learn to navigate in bitcoinland.
If you have enough money to invest, money your can afford to lose, then just buy bitcoin every month, sit on it, and in a few years you'll have a nice sum of money.
Thanks for the response. What are airdrops? and what examples of giveaways and where to source them?