You will not know for sure how much is the minimum, as it depends on the money that you dedicated to investing in the transaction. If it was me, it would be $ 200- $ 400. It is possible for you to be $ 2000- $ 4000. Wish you successful trading!
I know the guy, who entered the market with $15. Although it was a couple of years ago, it does not matter. Now, he is a successful trader, who makes really good money. Everything depends on your willingness to work.
Good for him. I think you can start trading at 0.005 BTC or lower depending on what exchanges you are in and you can go along with this. One important thing is you learn. Start small you will lose small also. I think its better to make your own research and invest on learning too.