It's because the purchase limit is 5 dollars, so it varies depending on the value of the real

Guys, I have 10 reais in my wallet. What is the minimum amount to invest? Some say 20, others say 25. Please help me. Or does it depend on the currency?

After reaching this minimum amount, which currency do I buy? I already have BTC and ETH. Should I keep them or can I change them?