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If I deposit $100 or $120 worth of bitcoins per month from here, how much will it benefit me? Is it right for me to invest more $ in Bitcoin than this? And should I invest the whole money in Bitcoin?
Don't invest the whole money, you don't have to start big when you're just getting started, you build up your asset in bitcoin gradually, its never a bad or wrong idea for you to start from that range, with time, it will turn to something amazing if you can hold.
It all depends on the individual's higher or lower degree of risk aversion, and his/her socioeconomic circumstances. In the case of students with no debt or other economic obligations, who earn a little money doing small jobs or thanks to a business idea, which seems to be the case, I don't think it's crazy to invest the whole money, since it is not so much, and other people at that age don't earn a think, only spend.
Just be aware, again, that crypto is risky investment and you can lose the money invested, or a good part of it, even if you stick to Bitcoin.