I think it is up to you and your trading strategy that how you are willing to invest. For instance, you can start with 500$ but I would like to advise do not to invest that much high amount of money at the beginning of your trading period until you are certain about the forex and have good knowledge and skills. First, start trading with a demo account to do practice and always be ready to learn more new things about forex.

There is no set rule, but I would suggest starting really low at first. There are even possible options where you can start with as little as $10. You cannot expect to do that well at first and since most likely you can end up making a loss at least it will be a really small amount that you lose in this way. As you said it is always ideal to start with a demo account so as to practise a bit. As time goes by you will feel more confident and experienced, and you can increase the amounts.

For beginners in Forex trading, it's crucial to start with an amount that they can afford to lose without significant financial repercussions. While there's no set amount, here are some considerations:

1. Risk Capital: Only invest what you can afford to lose. This ensures that any losses won't have a severe impact on your financial well-being.

2. Start Small: Begin with a modest amount, such as a few hundred dollars, to get a feel for the market and gain experience without exposing yourself to excessive risk.

3. Risk Management: Use proper risk management techniques, such as setting stop-loss orders and limiting the size of each trade to a small percentage of your total capital.

4. Education: Allocate a portion of your investment budget to education and training. Investing in learning resources, courses, and demo accounts can help you develop the necessary skills and knowledge to become a successful trader.

5. Gradual Increase: As you gain experience and confidence, you can gradually increase your investment amount over time. Always prioritize preserving capital and managing risk effectively.