Everyone asks this question but no one ever gives you an answer besides "as much as you are willing to lose" which is excellent advice thats what I do, but thats not a number.
everyone says that because it is true.
for example if I say $10,000 you will start running and screaming and if I say $0.02 you will burst out laughing but they are both true and you can use both numbers to start your trading. the first is ~2.22
BTC and second one is about 500 satoshi or the minimum order size of some exchanges!
My reasoning is this. The market swings up and down about $400USD a day.
the swings that big are so rare that they almost never happen.
The most you can make off a trade will be that number. It has to be worth your time. My minimum wage is $15/hr since adjusted for inflation that what US min wage is supposed to be.
if what you said were true then you would lose the same amount of the swings is not in your favor. so think about that for a while before wanting to invest $4000 as a start.
Anything less then 4000 is just a hobby.
no it really is not.
in fact one of the best things about this market is that you can start with a very small amount to try and learn things and build up your confidence and make all the mistakes you want. then increase the amount.
on top of it, when you become experienced enough you can make a big profit from altcoins that are getting pumped and earn a very good amount of profit in short term. even 100% profit. so if you invest $1000 you can make it into a $10000 potentially by the end of the month too.
in the end, it is not right to give a number because it can be very different for different people. I may prefer trading with only half abitcoin while others do it with 10 bitcoin and be happy. just do what you are more comfortable with.