Altcoins don't just follow in bitcoin's footsteps, but also multiply this effect many times over, especially when it comes to falling. If bitcoin falls by 10%, altcoins can lose 30-40%. There is a flip side to this effect as well. When bitcoin grows by 50%, altcoins can grow by 200%, but they also quickly become cheaper after such growth, so you need to sell quickly, otherwise all the price momentum will disappear as if it never happened.
Of course. Altcoins usually have higher fluctuations in market price. That's the reason why they're a much-riskier investment than Bitcoin itself. If you know how to play your cards right, you could make a lot more money with altcoins than Bitcoin alone. Most people like altcoins because they bring new features not found on the main Bitcoin blockchain. Not to mention, they're a lot cheaper than BTC.
Like I've said before, a promising altcoin is one that's not driven by hype but delivers as promised. Active development, innovation, and most importantly, real use cases is what makes an altcoin a solid long-term investment. I'd say ETH, LTC, ADA, and BNB are the "best of the best" in the crypto market. The rest are pure junk. This is my own opinion, and not investment advice. I'd advise you to do your own research to help determine what works best for you. As long as you don't turn greedy by putting all of your life savings into crypto, there should be nothing to worry about. Just my thoughts