There is no ideal number. My favorite advice is always this: Invest an amount that wouldn't hurt you financially even if you lost all of it. Although we all hope for the best and want to make profit, the crypto environment (especially the altcoin environment) is highly volatile and you never know what might happen tomorrow.
I agree. That's the beauty of the bitcoin market, you can actually start with it with little capital because there are some coins which are good enough to invest but you can buy for a price even lower than a dollars. You just have to be patient with your investment, and also, you have to be smart about it, so that would choose the better investments rather than the one-trick-ponies that may increase for one time but would not have any more in the future. Also, it would be actually better to start small and not invest all your money, since you are a beginner, you are bound to lose some of your investment in bad trades, thus, it would help mitigate your loses.