People seem to have become millionaires in previous bull cycles with modest investments in BTC & ETH. If I invested in 1 BTC, is it enough to make me a millionaire by the next bull run, or are there an elite number of alt coins that could help me safely achieve what BTC & ETH once did?
you should do your own research and look for projects with good potential, and guarantee your investment, you can just ask others for advice, but you should review before investing in the project.
asking other people to look for information does not necessarily mean that the project has potential, if you are ready to accept the risk of your friend's research results it is not a problem. because out there many people ask friends to find coins with long-term potential that is not a guarantee. Of course it's better to do your own research to be more confident about the risks that will come because it's the result of choosing your own research coin, learning from mistakes will improve material, broad experience