There's no specific amount laid down as a conventionally accepted figure needed to run a good bitcoin investment, all that's needed importantly is your knowledge and experience to use in running whatever amount you can afford to start with.
I partially agreed on your opinion, but the investment amount should be above 50$ to see least change on the investment. But there is no limit or barrier on investment in bitcoin.
Also, it is risky to invest on altcoins no matter newbie or you have enough knowledge in cryptocurrency.