It depends on your lifestyle. There's really no required minimum amount a poor person should have but it's on how they are going to determine what they need for the rest of their lives. Usually with these calculations, we're thinking on how much we can afford to live on a daily basis and how much we need for our eternity. But if you're going to be with reality, start with 1 bitcoin if you can but if not then reduce it to decimals that you can afford to. Like, 0.1, 0.01, 0.001 BTC and so on as you start. I'm talking about your start because not everyone can avail to buy an entire Bitcoin as they think. So it should be safe to say around 0.01 - 0.1BTC as the minimum.